{{Short description|Inland river delta and estuary in Northern California}} {{Use American English|date = January 2020}} {{Use mdy dates|date=March 2021}} [[Image:Wpdms usgs photo sacramento delta 2.jpg|thumb|Northern California's Sacramento–San Joaquin River Delta. The Sacramento River flows into the [[river delta|delta]] from the north and the [[San Joaquin River]] from the south through [[Stockton, California|Stockton]].]] [[Image:Islands,_Sacramento_River_Delta,_California.jpg|thumb|right|Part of the Delta viewed from above. [[Sherman Island (California)|Sherman Island]] in foreground with the Sacramento River above and San Joaquin River below/right.]]
The '''Sacramento–San Joaquin River Delta''', or '''California Delta''', is an expansive inland [[river delta]] and [[estuary]] in [[Central California]] and [[Northern California]]. The delta is formed at the western edge of the [[Central Valley (California)|Central Valley]] by the confluence of the [[Sacramento River|Sacramento]] and [[San Joaquin River|San Joaquin]] rivers and lies just east of where the rivers enter [[Suisun Bay]], which flows into [[San Francisco Bay]], then the [[Pacific Ocean]] via [[San Pablo Bay]]. The Delta is recognized for protection by the [[California Bays and Estuaries Policy]].<ref name="swrcb">{{cite book |author=State Water Resources Control Board |title=Water Quality Control Policy for the Enclosed Bays and Estuaries of California |publisher=State of California |year=1974}}</ref> Sacramento–San Joaquin Delta was designated a [[National Heritage Area]] on March 12, 2019. The city of [[Stockton, California|Stockton]] is located on the San Joaquin River at the eastern edge of the delta. The total area of the Delta, including both land and water, is about {{convert|1100|mi2|km2}}. Its population is around 500,000.<ref>{{Cite web|url=https://www.epa.gov/sfbay-delta/about|title=About the Watershed|last=US EPA|first=REG 09|date=December 4, 2012|website=US EPA|language=en|access-date=August 2, 2019|archive-date=August 2, 2019|archive-url=https://web.archive.org/web/20190802194340/https://www.epa.gov/sfbay-delta/about-watershed|url-status=live}}</ref>
The Delta was formed by rising sea level following glaciation, leading to the accumulation of Sacramento and San Joaquin River [[sediment]]s behind the [[Carquinez Strait]], the sole outlet from the Central Valley to San Pablo Bay. The narrowness of the Carquinez Strait coupled with tidal action has caused the sediment to pile up, forming expansive islands. Geologically, the Delta has existed for about 10,000 years, since the end of the [[Last Glacial Period]]. In its natural state, the Delta was a large freshwater [[marsh]], consisting of many shallow channels and sloughs surrounding low islands of peat and [[tule]].
Since the mid-19th century, most of the region has been gradually claimed for agriculture. Wind erosion and oxidation have led to widespread [[Land subsidence|subsidence]] on the Central Delta islands; much of the Delta region today sits below sea level, behind levees earning it the nickname "California's [[Netherlands|Holland]]".<ref>{{Cite web |url=https://pubs.usgs.gov/circ/circ1182/pdf/11Delta.pdf |title=Sacramento-San Joaquin Delta, U.S.G.S. |access-date=August 16, 2013 |archive-date=August 27, 2013 |archive-url=https://web.archive.org/web/20130827080336/http://pubs.usgs.gov/circ/circ1182/pdf/11Delta.pdf |url-status=live }}</ref><ref>{{cite news |url=https://www.latimes.com/archives/la-xpm-2010-nov-24-la-me-water-delta-20101125-story.html |title=Sacramento-San Joaquin Delta's ecological decline is breathing new life into bypass proposals: A plan for a huge tunnel is the leading contender as the state looks for a way to save the delta at the same time it slakes thirsts in Southern California. |work=Los Angeles Times |author=Boxall, Bettina |date=November 24, 2010 |access-date=August 15, 2013 |archive-date=October 1, 2013 |archive-url=https://web.archive.org/web/20131001085732/http://articles.latimes.com/2010/nov/24/local/la-me-water-delta-20101125 |url-status=live }}</ref> Much of the water supply for [[Central California]] and [[Southern California]] is also derived from the Delta, via pumps located at the southern end of the Delta. The pumps deliver water for irrigation in the [[San Joaquin Valley]] and municipal water supply for Southern California.
==Geography== {{Islands of Suisun Bay and the Sacramento–San Joaquin River delta|.}} [[Image:SanJoaquinOldRiver.jpg|thumb|left|The Old River, a former channel of the San Joaquin River located in the southwestern Delta]] {{See also|List of islands of California#Sacramento–San Joaquin River Delta}} The Delta consists of approximately 57 reclaimed islands and tracts but there are nearly 200 islands in the delta that are named or not named. These are all surrounded by {{convert|1100|mi|km}} of levees that border {{convert|700|mi|km}} of waterways.<ref name="DWR">{{cite web |url=http://www.water.ca.gov/swp/delta.cfm |title=Where Rivers Meet-The Sacramento-San Joaquin Delta |publisher=California Department of Water Resources |work=State Water Project |date=July 18, 2008 |access-date=August 15, 2013 |archive-date=July 1, 2013 |archive-url=https://web.archive.org/web/20130701221851/http://www.water.ca.gov/swp/delta.cfm |url-status=live }}</ref> The southwestern side of the Delta lies at the foothills of the [[California Coast Ranges]], while to the northwest sit the lower [[Montezuma Hills]]. Most of the Delta lies within [[Contra Costa County, California|Contra Costa]], [[Sacramento County, California|Sacramento]], [[San Joaquin County, California|San Joaquin]], [[Solano County, California|Solano]] and [[Yolo County, California|Yolo]] Counties.<ref>{{cite web |url=http://www.sacramentoriverdelta.net/delta-counties-coalition/ |title=Delta Counties Coalition |publisher=Sacramento River Delta |access-date=August 15, 2013 |archive-date=April 23, 2014 |archive-url=https://web.archive.org/web/20140423112225/http://www.sacramentoriverdelta.net/delta-counties-coalition/ |url-status=live }}</ref> The total human population of the Delta was 515,264 as of 2000.<ref name="DWR"/>
Altogether, the Delta covers {{convert|1153|mi2|km2}}, with {{convert|841|mi2|km2|abbr=on}}, or nearly 73 percent, devoted to agriculture. About {{convert|100|mi2|km2|abbr=on}} of the Delta area is urban and {{convert|117|mi2|km2|abbr=on}} are undeveloped land. The rivers, streams, sloughs and waterways of the Delta total about {{convert|95|mi2|km2|abbr=on}} of surface, although this fluctuates greatly with seasons and tides.<ref name="DWR"/> Geologically, it is not considered a true river delta, but rather an [[inverted river delta]], as it formed inward (sediments accumulating progressively inland) rather than outward. The only other major river delta in the world located this far inland is the [[Pearl River Delta]] in China.<ref name="Reisner18">Reisner, p. 18</ref>
The main source rivers include the Sacramento River from the north, the San Joaquin from the southeast, and the [[Calaveras River|Calaveras]] and [[Mokelumne River]]s from the east. The Calaveras and Mokelumne are both tributaries of the San Joaquin River. The Sacramento and San Joaquin Rivers join at the western end of the Delta near [[Pittsburg, California|Pittsburg]], at the head of Suisun Bay, although they are linked upstream by the [[Georgiana Slough]], which was first used by steamboats in the 19th century as a shortcut between [[Sacramento, California|Sacramento]] and [[Stockton, California|Stockton]]. The southwestern part of the Delta is also transected by the Middle River and Old River, former channels of the San Joaquin. These rivers transport more than {{convert|30|e6acre.ft|mi3 km3}} of water through the Delta each year – about 50 percent of all California's runoff.<ref name="factsheet">{{cite web |url=https://pubs.usgs.gov/fs/2000/fs00500/pdf/fs00500.pdf |title=Delta Fact Sheet |publisher=U.S. Geological Survey |year=2000 |access-date=August 15, 2013 |archive-date=July 10, 2011 |archive-url=https://web.archive.org/web/20110710224624/http://pubs.usgs.gov/fs/2000/fs00500/pdf/fs00500.pdf |url-status=live }}</ref>
Nearby cities include [[Lodi, California|Lodi]] and Stockton to the east, [[Tracy, California|Tracy]] and [[Manteca, California|Manteca]] to the south, [[Brentwood, California|Brentwood]] to the southwest, and Pittsburg and [[Antioch, California|Antioch]] to the west. The state capital, [[Sacramento, California|Sacramento]], is located just to the north of the Delta.<ref>{{cite map |title=The National Map |cartography=USGS |publisher=U.S. Geological Survey |year=2013 |url=http://viewer.nationalmap.gov/viewer/ |access-date=August 16, 2013 |archive-date=March 29, 2012 |archive-url=https://web.archive.org/web/20120329155652/http://viewer.nationalmap.gov/viewer/ |url-status=live }}</ref>
The [[Sacramento River Deep Water Ship Channel]] connects the Delta to the [[Port of Sacramento]], with its terminus located near [[Rio Vista, California|Rio Vista]], on the northwestern side of the Delta. The [[San Joaquin River#Stockton Ship Channel|Stockton Ship Channel]] is a dredged and partially straightened section of the [[San Joaquin River]] cutting directly through the Delta from the [[Port of Stockton]] to the San Joaquin's confluence with the Sacramento near Antioch.{{Citation needed|date=July 2018}}
==Geology, formation and natural conditions== {{Quote box |width=18em |align=left |quote="The virgin California Delta was so vast, wild and confusing – its sloughs meandered everywhere and led nowhere – that [[John C. Frémont]] lost a whole regiment in there for several days, and some who ventured in just disappeared."|source=[[Marc Reisner]], ''A Dangerous Place'' (2003)<ref name="Reisner18"/>}} The Delta was formerly located at the bottom of a large inland sea in the Central Valley, which formed as the uplift of the [[California Coast Ranges]] blocked off drainage from the [[Sierra Nevada (U.S.)|Sierra Nevada]] to the Pacific. About 560,000 years ago, water breached the mountains, carving out the present-day [[Carquinez Strait]] and [[San Francisco Bay]]. The drainage of all the water through this narrow gap formed a bottleneck in the Central Valley's outflow; this constriction is essential to provoke the slowing of river current and the resulting sediment deposits that now make up the Delta.<ref>{{cite web |url=http://education.savingthebay.org/wp-content/guides/The-Formation-of-San-Francisco-Bay.pdf |title=The Formation of San Francisco Bay |publisher=Saving the Bay |access-date=August 20, 2013 |archive-date=July 19, 2014 |archive-url=https://web.archive.org/web/20140719092249/http://education.savingthebay.org/wp-content/guides/The-Formation-of-San-Francisco-Bay.pdf |url-status=live }}</ref>
The Delta in its contemporary (pre-1850s) state began to form about 10,000 years ago at the end of the last Ice Age. During the Ice Age global sea levels were about {{convert|300|ft|m|abbr=on}} lower than today, and the Delta region, as well as Suisun Bay, the Carquinez Strait and San Francisco Bay, were a river valley through which the continuation of the Sacramento and San Joaquin Rivers flowed to the Pacific Ocean. When sea levels rose again, ocean water backed up through the Carquinez Strait into the Central Valley; the combination of the narrow strait and tidal action pushing inland dramatically slowed the current of these rivers and forced them to drop sediment. <!--This resulted in the formation of an inland or inverse river delta, in which multiple incoming rivers merge into one, rather than a conventional river delta, where one river splits into multiple channels that flow to the sea.--> The early delta was composed of shifting channels, sand dunes, alluvial fans and floodplains that underwent constant fluctuation because of rapidly rising seas – {{Convert|1|inch|spell=in}} per year. About 8,000 years ago, the rate of sea-level rise slackened, allowing wetland plants to take hold in the Delta, trapping sediment; the growth and decay of these plants began to form the vast peat deposits that make up the Delta islands. The Delta reached a stabilized form similar to its mid-1800s state about 2,000–3,000 years ago.<ref>Pierce, pp. 4–5</ref> [[Image:SacDelta1.jpg|thumb|right|450px|An 1850 drawing of the Sacramento River in the Delta, showing the lush foliage that made up much of the virgin Delta.]]
Immediately before large-scale human development, most of the Delta islands had saucer-like cross sections, with low natural levees flanking a marshy interior "bowl" that flooded intermittently with the seasons and tides. The height of these natural levees, formed from overbank deposits of sediments deposited by annual river floods, ranged from {{convert|1|ft|m|spell=in}} above mean high tide at [[Sherman Island (California)|Sherman Island]] on the Sacramento River, to {{convert|7|to|8|ft|m|spell=in}} at [[Andrus Island|Andrus]], [[Staten Island (California)|Staten]] and Tyler Islands, located further east near the Mokelumne River. An estimated 60 percent of the Delta flooded for up to two hours each day at high tide;<ref name="history"/> during [[spring tide]]s or river floods, it was not uncommon for the entire Delta to be under water.<ref>Thompson, pp. 45–46</ref>
==History== Humans have inhabited the Delta for up to 4,300 years.<ref>Pierce, p. 11</ref> The estimated indigenous population of the Delta at the time of first contact with Europeans was about 3,000–15,000, predominantly [[Miwok people|Miwok]] and [[Maidu]],<ref name="history">{{cite web |url=http://www.planning.org/planning/2012/jan/waterwarriorsside1.htm |title=The Devil Is in the Delta: Can California's Sacramento-San Joaquin river delta be saved? The state's cities and farms hope the answer is yes, but no one is in charge. |publisher=American Planning Association |date=January 2012 |author=Shigley, Paul |access-date=August 20, 2013 |archive-date=September 10, 2013 |archive-url=https://web.archive.org/web/20130910062340/http://www.planning.org/planning/2012/jan/waterwarriorsside1.htm |url-status=live }}</ref> with some estimates ranging up to 20,000.<ref name="short-history">{{cite web |url=http://californiadeltaevents.com/commodore-corner/2012/09/03/1448/a-short-history-of-the-delta-part-1/ |title=A Short History of the Delta (Part 1) |publisher=California Delta Events |work=Commodore's Corner |access-date=August 20, 2013 |archive-date=November 13, 2012 |archive-url=https://web.archive.org/web/20121113225258/http://californiadeltaevents.com/commodore-corner/2012/09/03/1448/a-short-history-of-the-delta-part-1/ |url-status=live }}</ref> The Native Americans lived in villages of 200–1,000 people on the eastern edge of the Delta, where the land was higher and less susceptible to flooding. Their lives centered around the abundant reeds or tules that grew on the Delta islands, which they used to make houses, boats, and garments.<ref name="history"/> Staple foods included tule roots and pollen, acorns, wild fruits and seeds, fish and game.<ref name="legacies"/>
Europeans first entered the Delta region in 1772, when Spanish explorer [[Don Pedro Fages]] and missionary [[Juan Crespí]] observed the Delta from the summit of nearby [[Mount Diablo]]. For decades, the Delta was little utilized by the Spanish colonists. Expeditions from 1806 to 1812 failed to locate suitable [[Missions of California|mission]] sites in the Delta area. However, frequent military expeditions were made into the Delta from 1813 to 1845 in response to animosities between the Native Americans and the Spanish and later Mexicans; also several land grants were made in the vicinity of the Delta, including one to [[John Augustus Sutter]], who started the first significant European settlement in the Central Valley just north of the Delta near present-day Sacramento.<ref name="legacies">{{cite web |author=Lund, Jay |url=http://www.ppic.org/content/pubs/report/R_207JLChapter2R.pdf |title=The Legacies of Delta History |publisher=Public Policy Institute of California |work=Envisioning Futures for the Sacramento-San Joaquin Delta |date=February 2007 |access-date=August 19, 2013 |display-authors=etal |archive-date=October 1, 2013 |archive-url=https://web.archive.org/web/20131001081942/http://www.ppic.org/content/pubs/report/R_207JLChapter2R.pdf |url-status=live }}</ref>
[[Image:Map of the San Joaquin, Sacramento and Tulare Valleys 1873.jpg|thumb|right|An 1873 map showing the river systems of the Central Valley, with wetlands marked in gray. The Delta, at roughly left center, was the largest area of contiguous, perennial wetlands in pre-development California.]] The Spanish conscripted large numbers of Native Americans for labor on missions; many Native Americans fled deep into the Delta in order to escape their European masters. However, this did not protect them from diseases. A [[malaria]] epidemic in 1833 decimated local native populations; this was probably exacerbated by the marshy geography of the area, which bred large amounts of mosquitoes.<ref name="short-history"/>
The agricultural value of the Delta was first recognized during the [[California Gold Rush]], when farmers planted orchards on Delta islands to provide fresh fruit for mining camps in the [[Sierra Nevada (U.S.)|Sierra Nevada]].<ref>Reisner, pp. 18–19</ref> Because of the flat terrain coupled with year-round availability of fresh water, irrigation here was cheaper and simpler than other fertile regions of California. As a result, the Delta remained California's richest farming region (alongside [[Los Angeles County, California|Los Angeles County]]) until the 1940s, when massive federal water projects finally made possible the full-scale irrigation of the main body of the Central Valley. Today, the Delta is still among the state's most productive farming regions.<ref name="restore">{{cite web |url = http://www.restorethedelta.org/about-the-delta/overview-of-delta-agriculture/ |title = Overview of Delta Agriculture |publisher = Restore The Delta |access-date = August 19, 2013 |url-status = dead |archive-url = https://web.archive.org/web/20130310052106/http://www.restorethedelta.org/about-the-delta/overview-of-delta-agriculture/ |archive-date = March 10, 2013 }}</ref>
In 1850, Congress passed the Arkansas or [[Swamp Land Act of 1850|Swampland Act]], which allowed for the transfer of title for wetlands to private owners on the conditions that the land would be reclaimed. In California, more than {{convert|2|e6acre|sqmi km2|spell=in}} of wetlands were partitioned under the Swampland Act, of which {{convert|500000|acre|sqmi km2}} were in the Sacramento–San Joaquin Delta, roughly the same amount of land that has been developed to date.<ref name="agriculture">{{cite web |url=http://ucce.ucdavis.edu/files/repositoryfiles/ca3311p4-62696.pdf |title=Agriculture in the Sacramento-San Joaquin Delta |publisher=University of California Davis |work=California Agriculture Journal |year=1979 |access-date=August 19, 2013 |archive-date=July 20, 2014 |archive-url=https://web.archive.org/web/20140720182125/http://ucce.ucdavis.edu/files/repositoryfiles/ca3311p4-62696.pdf |url-status=live }}</ref> Agricultural interests in the Delta were protected by the building of levees, a colossal effort first undertaken by Chinese laborers from the 1850s to the 1870s. The Board of Reclamation, formed in 1861, collectivized levee construction in the Delta by grouping islands into areas known as ''[[California Reclamation Districts|reclamation districts]]''.<ref name="legacies"/> The early levees were built of peat, and were highly susceptible to wind and water erosion. The [[Great Flood of 1862]] obliterated much of the existing Delta infrastructure, forcing landowners to rebuild their levees higher and stronger; more flooding in 1878 and 1881 reinforced these notions.<ref name="legacies"/><!--A typical levee was constructed as being approximately trapezoidal, {{convert|10|ft|m|abbr=on}} above original ground level, and approximately {{convert|30|ft|m|abbr=on}} wide at the base, rock-armored on the river side.-->
Although land holdings in the Delta were initially limited to {{convert|320|acre|sqmi km2}} per buyer, this limit was repealed in 1868, allowing large agricultural conglomerates to take entire islands and carry out massive reclamation projects. From 1868 to 1869, the entirety of Sherman Island, some {{convert|14000|acre|sqmi km2}}, was diked and drained by a system of levees, flumes and floodgates.<ref>Thompson, p. 48</ref> By the 1890s, the original levee system had been largely replaced with stronger embankments consisting of clay dredged from nearby river bottoms.<ref>Thompson, p. 43</ref> By 1900, about {{convert|235000|acre|sqmi km2}}, or nearly half of the Delta's land area, had been reclaimed.<ref name="legacies"/> Most of the farmable land in the Delta had been reclaimed by the 1920s.<ref name="agriculture"/>
==Economy and human use==
===Agriculture=== The Delta produces crops valued at about $650 million annually (for the 1998–2004 period),<ref>{{cite web|url=http://deltavision.ca.gov/Context_Memos/Agriculture/Agriculture_Iteration2.pdf|title=Context Memorandum: Agriculture in the Delta|publisher=Delta Vision|date=August 10, 2007|access-date=February 9, 2017|archive-date=January 25, 2017|archive-url=https://web.archive.org/web/20170125033523/http://deltavision.ca.gov/Context_memos/Agriculture/Agriculture_Iteration2.pdf|url-status=live}}</ref> making it one of the most productive farming regions of the United States in terms of crop value per unit area. Agriculture provides secondary benefits of over $2 billion to the local economy.<ref name="restore"/> Major crops grown in the Delta include corn, grain, hay, sugar beets, alfalfa, tomatoes, asparagus, and safflower; various fruits are also raised here, as well as some livestock.<ref name="DWR"/> Crops in the Delta cannot be irrigated using conventional methods due to the highly absorbent quality of the peat soil and irregularities caused by land subsidence. Irrigation is typically carried out periodically by piping water into small "spud ditches", which spread water over large areas and raise the local [[water table]]. The heightened groundwater is then gradually depleted by the crop until irrigation is required again.<ref name="agriculture"/>
===Transportation=== Delta waterways are also major transportation corridors for agricultural products; the ports of [[Port of Sacramento|Sacramento]] and [[Port of Stockton|Stockton]], located on the Sacramento and San Joaquin rivers, respectively, are the most important inland ports in California. The San Joaquin River throughout most of the Delta and the lower Sacramento River below its connection to the [[Sacramento Deep Water Ship Channel]] are routinely dredged to allow the passage of large cargo ships. The Sacramento River corridor has been maintained to a depth of {{convert|7|ft|m|abbr=on}} as early as 1899, and was deepened to {{convert|30|ft|m|abbr=on}} in 1955. The [[San Joaquin River#Stockton Ship Channel|Stockton Ship Channel]] has been dredged since 1913; however, its present depth of {{convert|37|ft|m|abbr=on}} was only achieved in 1987.<ref name="legacies"/> The Delta is also home to the port of [[Benicia, California|Benicia]], an automobile and bulk shipping facility.<ref>[http://www.dot.ca.gov/hq/tpp/offices/ogm/ships/Fact_Sheets/Port_of_Benicia_Fact_Sheet_073012.pdf ''Freight Planning Fact Sheet: Port of Benicia''] {{Webarchive|url=https://web.archive.org/web/20170429075221/http://www.dot.ca.gov/hq/tpp//offices/ogm/ships/Fact_Sheets/Port_of_Benicia_Fact_Sheet_073012.pdf |date=April 29, 2017 }}, California Dept. of Transportation, Caltrans Office of System and Freight Planning, July 2012, retrieved November 24, 2018.</ref> Petroleum is shipped to both the [[Benicia Refinery]] and the [[Golden Eagle Refinery|Martinez Refinery]] by water. Nearby is the [[Port Chicago, California|Port Chicago Marine Ocean Terminal]], a facility that supports the U.S. Navy.
===Water supply=== [[Image:Water_in_California_new.png|thumb|left|300px|The Delta (located south of Sacramento, middle left, at the confluence of the Sacramento and San Joaquin rivers) is central to California's water supply system.]] The Delta is often considered the nexus of [[Water in California|California's statewide water system]].<ref name="subsidence"/><ref>{{cite web |url=http://www.water.ca.gov/deltainit/ |title=Delta Initiatives |publisher=California Department of Water Resources |access-date=August 16, 2013 |archive-date=September 10, 2013 |archive-url=https://web.archive.org/web/20130910182854/http://www.water.ca.gov/deltainit/ |url-status=live }}</ref> About half the total river flow in the state passes through this region, from which water is exported to other areas of the San Joaquin Valley, Southern California and portions of the Bay area to supply some {{convert|1130000|acre|sqmi km2|abbr=on}} of farmland and 23 million people in central and Southern California.<ref>{{cite web |url=http://www.acwa.com/content/delta/californias-water-sacramento-san-joaquin-river-delta-0 |title=California's Water: Sacramento-San Joaquin River Delta |publisher=Association of California Water Agencies |access-date=August 19, 2013 |archive-date=October 1, 2013 |archive-url=https://web.archive.org/web/20131001075611/http://www.acwa.com/content/delta/californias-water-sacramento-san-joaquin-river-delta-0 |url-status=live }}</ref> The Delta provides an estimated {{convert|7|e6acre.ft|cumi km3|spell=in}} of water per year, of which about {{convert|100000|acre.ft|cumi km3}} are exported to the San Francisco Bay Area, {{convert|1.7|e6acre.ft|cumi km3}} are used locally, and over {{convert|5|e6acre.ft|mi3 km3|spell=in}} are exported to the San Joaquin Valley, coastal Central and Southern California.<ref name="factsheet"/>
Intrusion of brackish water into the Delta is a recurring natural phenomenon; however, it became a serious issue after the development of agriculture in the upper Sacramento and San Joaquin valley reduced inflows. Multiple droughts between 1910 and 1940 caused significant salinity intrusion in the Delta because of the reduction of freshwater inflows. The growing Delta water quality issue provided the initial impetus for building dams on Central Valley rivers to boost dry-season freshwater flows. This eventually became the federal [[Central Valley Project]] (CVP), California's first major statewide water system, most of which was built between the 1930s and the 1960s.<ref>{{cite web |url=http://www.usbr.gov/projects/Project.jsp?proj_Name=Central+Valley+Project |title=Central Valley Project |publisher=U.S. Bureau of Reclamation |date=March 15, 2013 |access-date=August 20, 2013 |archive-date=June 15, 2011 |archive-url=https://web.archive.org/web/20110615004945/http://www.usbr.gov/projects/Project.jsp?proj_Name=Central%20Valley%20Project |url-status=dead }}</ref>
Today, the [[California Aqueduct]] and the [[Delta-Mendota Canal]], two of the state's largest water conveyance facilities, both draw water from the southern end of the Delta at the [[Clifton Court Forebay]]. Built in the mid-twentieth century, the former supplies water to the [[Los Angeles Basin]] and coastal central California via the [[State Water Project]]; the latter, a part of the CVP, provides supplies of irrigation water in the fertile San Joaquin Valley. Although the vast majority of water supplied by these projects is used for agriculture and urban areas, some water is also provided for wildlife refuges and habitat conservation works.<ref>{{cite web |url=http://www.sldmwa.org/about_sldmwa.htm |title=Background |publisher=San Luis & Delta-Mendota Water Authority |access-date=August 16, 2013 |archive-date=September 4, 2013 |archive-url=https://web.archive.org/web/20130904040853/http://www.sldmwa.org/about_sldmwa.htm |url-status=live }}</ref> The [[Contra Costa Canal]] and [[North Bay Aqueduct]] also take Delta water, supplying the nearby San Francisco Bay Area. Locally, the Delta provides water for cities and towns in five counties and for over 1,800 agricultural users.<ref name="DWR"/>
=== Recreation === The Delta is also a popular site for recreation and is used for sailing, waterskiing, houseboating, fishing, and hunting.<ref name=":0">{{cite web |website=California State Parks Planning Division|title=Recreation Proposal for the Sacramento-San Joaquin Delta and Suisun Marsh|date=2011|url=http://www.parks.ca.gov/pages/795/files/delta%20rec%20proposal_08_02_11.pdf |archive-url=https://web.archive.org/web/20190223195208/http://www.parks.ca.gov/pages/795/files/delta%20rec%20proposal_08_02_11.pdf |archive-date=February 23, 2019|access-date=November 23, 2018}}</ref> The Delta is home to over 100 marinas and 25 yacht clubs. In 2010, over seven million 'annual visitor boating days' occurred on the Delta, according to a local government survey.<ref name=":0" />
The Delta is home to several state and regional parks, reflecting a variety of recreational activities. These include historical interpretative centers, including [[Locke, California|Delta Meadows and Locke Boarding House]] and the [[Old Sacramento State Historic Park]]. The [[Port Chicago Naval Magazine National Memorial]] offers visitors a chance to learn about the [[Port Chicago disaster|disaster]] that represented the largest domestic loss of life in the U.S. in World War II, and the impact it had on race relations in the U.S. military.
[[Brannan Island State Recreation Area]] offers boat launches and facilities that support fishing, windsurfing, waterskiing, and sailing, in addition to campsites, picnic areas and trails to allow visitors to explore the marshes and islands of the area.<ref>{{Cite web|url=https://www.parks.ca.gov/?page_id=487|title=Brannan Island SRA|last=California|first=California State Parks, State of|website=CA State Parks|language=en|access-date=November 24, 2018|archive-date=November 25, 2018|archive-url=https://web.archive.org/web/20181125074019/https://www.parks.ca.gov/?page_id=487|url-status=live}}</ref>
Originally a Delta farming island, Franks Tract flooded in 1936 and again in 1938. The levees were never repaired and the island remained submerged, becoming an expanse of open water dotted with remnants of the original levees now the only landforms. In 1959, the area became a state park. [[Franks Tract State Recreation Area]] is accessible only by water and is used for fishing, waterfowl hunting, and boating.<ref>{{Cite web|url=https://www.parks.ca.gov/?page_id=490|title=Franks Tract SRA|last=California|first=California State Parks, State of|website=CA State Parks|language=en|access-date=November 25, 2018|archive-date=December 1, 2018|archive-url=https://web.archive.org/web/20181201214242/http://www.parks.ca.gov/?page_id=490|url-status=live}}</ref>
The [[Pacific Flyway]], a north–south route for migratory birds, crosses the Delta. The migratory birds provide both birdwatching and hunting opportunities. Including the northern [[Suisun Marsh]], there are over 150 private duck clubs in the area.<ref name=":0" />
==Effects of the levee system and freshwater diversion== [[Image:Land Subsidence in the Delta Eric Chase 1995.jpg|thumb|Land subsidence in the Delta as of 1995]] The levee system allowed farmers to drain and reclaim almost {{convert|500000|acre|sqmi km2}} of the Delta, then a tidal marsh. Once the rivers were confined to their riverbeds, the peat soil of the former tidal marsh was exposed to oxygen. As the oxygen-rich peat soil decomposed and then released carbon dioxide, profound [[Groundwater-related subsidence|subsidence]] of the land resulted, of up to 25 feet since the late 1800s.<ref>{{Cite web|url=https://baynature.org/article/want-to-prevent-californias-katrina-grow-a-marsh/|title=Want to Prevent California's Katrina? Grow a Marsh|last=Velasquez-Manoff|first=Moises|website=Bay Nature|language=en-US|access-date=October 19, 2019|archive-date=October 19, 2019|archive-url=https://web.archive.org/web/20191019121626/https://baynature.org/article/want-to-prevent-californias-katrina-grow-a-marsh/|url-status=live}}</ref>
Currently, most of the Delta is below sea level, with a great deal of the western and central Delta at least {{convert|15|ft|m}} below sea level. The [[California Department of Water Resources]] has experimented with re-flooding areas for [[wetland restoration]], in order to [[Carbon sequestration|sequester carbon]] and rebuild [[Soil health|soil levels]].<ref name=":1" /> In addition, shallow flooding of land to restore [[Anaerobic organism|anaerobic]] conditions is used as a [[sedimentation enhancing strategy]] to reduce subsidence and restore the wetlands in the Delta.<ref name=":12">{{Cite journal|last1=Miller|first1=R.|last2=Fram|first2=M. S.|last3=Fuji|first3=R.|last4=Wheeler|last5=G.|date=2008|title=Subsidence reversal in a re-established wetland in the Sacramento-San Joaquin Delta, California, USA|url=http://escholarship.org/uc/item/5j76502x|journal=San Francisco Estuary and Watershed Science|volume=6|issue=3|doi=10.15447/sfews.2008v6iss3art1|doi-access=free|access-date=March 15, 2021|archive-date=March 26, 2021|archive-url=https://web.archive.org/web/20210326053340/https://escholarship.org/uc/item/5j76502x|url-status=live}}</ref>
Land subsidence has endangered the Delta's system of protective levees, occasionally triggering levee failure and subsequent flooding.<ref>Reisner, pp. 21–22</ref><ref>{{cite web |url=http://www.water.ca.gov/floodsafe/fessro/subsidence.cfm |title=Subsidence in the Sacramento-San Joaquin Delta |publisher=California Department of Water Resources |date=July 24, 2012 |access-date=August 20, 2013 |archive-date=October 1, 2013 |archive-url=https://web.archive.org/web/20131001025713/http://www.water.ca.gov/floodsafe/fessro/subsidence.cfm |url-status=live }}</ref>
{{Quote box |width=18em |align=left |Using the Delta as the primary valve in a linear water system may have been convenient for a period, but that convenience has come at a high price for the environment.|source=—Paul Shigley, ''The Devil Is in the Delta'' (2012)<ref name="history"/>}}
Land subsidence also allows brackish water intrusion into the Delta, an issue compounded by the diversion of up to 25% of the freshwater flowing into the Delta. The decreased volume of freshwater in the Delta has had a profound effect on its ecology.<ref>{{cite web |url=https://www.pbs.org/newshour/rundown/2012/08/californias-mixing-bowl-the-deltas-crucial-role-in-a-thirsty-state.html |title=California's Mixing Bowl: The Delta's Crucial Role in a Thirsty State |author=Harless, William |publisher=PBS Newshour |date=August 2, 2012 |access-date=August 21, 2013 |archive-date=August 21, 2013 |archive-url=https://web.archive.org/web/20130821011221/http://www.pbs.org/newshour/rundown/2012/08/californias-mixing-bowl-the-deltas-crucial-role-in-a-thirsty-state.html |url-status=dead }}</ref> In most years, large dams in the Delta watershed fully hold back spring runoff; as a result the Delta is most susceptible to salinity intrusion between February and June. However, regulation provided by dams helps boost freshwater flows during dry summers and autumns, reducing the risk of salinity intrusion in these months.<ref name="factsheet"/><ref>{{cite web |url = https://pubs.usgs.gov/fs/2000/fs00500/pdf/fs00500.pdf |title = Delta Subsidence in California: The sinking heart of the State |work = [[United States Geological Survey]] |publisher = ca.water.usgs.gov |access-date = July 26, 2009 |url-status = live |archive-url = https://web.archive.org/web/20110710224624/http://pubs.usgs.gov/fs/2000/fs00500/pdf/fs00500.pdf |archive-date = July 10, 2011 |df = mdy-all }}</ref>
Diversions located at the southern end of the Delta, however, have negated some of the benefits of upstream dams. The powerful pumps that supply water for the Central Valley Project and State Water Project cause water in the Delta to flow from north to south instead of the natural direction of east to west. This has caused multiple environmental issues, such as the disruption of fish migration and salinity buildup in the eastern Delta, where salts can no longer be flushed to the sea by natural river flows.<ref name="history"/>
==Levee failures== [[File:Sacramento Delta at flood stage, 2009.jpg|thumb|Sacramento–San Joaquin Delta at flood stage, spring 2009. Photo by [[Doc Searls]].]] Since 1900, there have been over 160 [[Levee breach|levee failures]] in the Sacramento–San Joaquin River Delta. These numbers include multiple failures of a single levee structure. Levee failures, also known as breaches, can be caused by [[Levee breach#Overtopping|overtopping]] or [[structural failure]]. One of the most recent examples of levee failure in the Sacramento–San Joaquin River Delta occurred in June 2004 when a levee breach caused more than {{Convert|150000|acre-feet|}} of water to flood the entire island of [[Jones Tract]].<ref name="Department of Water Resources, State of California">{{cite web|title=Levee Failures in the Sacramento-San Joaquin River Delta|url=http://www.water.ca.gov/floodmgmt/docs/DeltaLeveeFailures_FMA_200709.pdf|publisher=California Department of Water Resources|access-date=August 20, 2012|archive-date=September 4, 2012|archive-url=https://web.archive.org/web/20120904090647/http://www.water.ca.gov/floodmgmt/docs/DeltaLeveeFailures_FMA_200709.pdf|url-status=live}}</ref>
But, the significant improvements made to the Delta levee system since 1982 have reduced the incidence of failures to this one major failure in 30 years. The most up-to-date description and discussion of the Delta levee system can be found in the Economic Sustainability Plan of the Delta Protection Commission.<ref>{{cite web|url=http://forecast.pacific.edu/desp.html|title=Center for Business and Policy Research|access-date=December 16, 2013|archive-date=April 5, 2013|archive-url=https://web.archive.org/web/20130405085945/http://forecast.pacific.edu/desp.html|url-status=live}}</ref> This study concluded that the Delta levee system is now relatively robust but should be improved to effectively eliminate the risk of failure in extreme floods and earthquakes. It emphasizes the significant value of the infrastructure that passes through the Delta, including water conveyance, in addition to life and property, and the value of the Delta as a Place.{{Citation needed|date=July 2018}}
A 2019 article states that "a catastrophic levee failure, defined as 20 islands flooding at once, has a 62 percent chance of occurring in the next two decades if subsidence isn’t addressed."<ref name=":1" />
Simultaneous levee failures on the Delta's 57 islands in the wake of an [[List of earthquakes in California|earthquake]] which allow the inflow of [[Brackish water|brackish]] San Francisco Bay waters could threaten the water supply for the [[Central Valley (California)|Central Valley]], which includes both the irrigation water for its $17 billion agricultural economy and the drinking water for about 25 million people.<ref name=":1" />
==Ecology== About 500 plant and animal species inhabit the Delta, which is one of the largest [[estuary|estuaries]] in western North America.<ref name="DWR"/> Before agricultural development of the Delta region, the Delta's many islands were forested by [[Schoenoplectus acutus|Tule]], [[bulrush]], and various reeds that flourished in intermittently flooded, low-lying marshy areas. Over thousands of years, the growth and decay of the various swampland plants formed a layer of peat {{convert|50|ft|m}} deep in places, hence the extremely high fertility of Delta soils.<ref>Reisner, p. 20</ref> Sediment deposits formed natural levees around the borders of islands, where larger trees, mainly willows,<ref>Thompson, p. 44</ref> were able to take root and form large [[riparian zone|riparian forests]].<ref name="factsheet"/> The riparian forests were most pronounced along the Sacramento River and the lower Mokelumne River below its confluence with the [[Cosumnes River]].<ref>Pierce, p. 7</ref> More extensive woodlands were prominent on the fringes of the Delta bordering the riparian zones. Composed primarily of [[valley oak]], [[box elder]] and [[Oregon ash]], these oak woodlands grew in bands that stretched up to {{convert|3|mi|km}} inland. Farther away from water sources, vegetation gave way to [[grassland]].<ref>Pierce, pp. 8–9</ref> The [[water hyacinth]] has become one of the most destructive plants to the Delta water way. Within one year it will spread and cover as much as {{Convert|6500|sqft|}} of water space in one growing season. It has become a challenge to the agricultural community to eliminate. The plants spread by budding and spreading its seeds, and those seeds fall to the bottom of the water, where they can stay viable in the muck for years. The Hyacinth can form a mat up to {{Convert|6|feet|}} thick, shutting off light and becoming acidic when they decompose.<ref>"Water Hyacinth" Tegtmeier</ref> [[Image:Hypomesus transpacificus.jpg|thumb|left|The tiny [[Delta smelt]] is an [[Endangered Species Act]] threatened species that has caused controversy over the amount of water that can be sustainably pumped from the Delta.]] The Delta was formerly populated by large herds of [[deer]] and [[tule elk]]; their trails were so vast that early Spanish explorers supposed the area was inhabited by cattle.<ref name="subsidence">{{cite web |author1=Ingebritsen, S.E. |author2=Ikehara, Marti E. |url=https://pubs.usgs.gov/circ/circ1182/pdf/11Delta.pdf |title=Sacramento-San Joaquin Delta: The sinking heart of the state |publisher=United States Geological Survey |work=Drainage of Organic Soils |access-date=August 15, 2013 |archive-date=August 27, 2013 |archive-url=https://web.archive.org/web/20130827080336/http://pubs.usgs.gov/circ/circ1182/pdf/11Delta.pdf |url-status=live }}</ref> Significant numbers of [[California grizzly|California grizzly bears]] could also be found in the Delta.<ref name="legacies"/> The extensive wetlands of the Delta supported massive bird populations,<ref name="subsidence"/> half the migrating waterfowl in California continue to pass through the Delta.<ref name="pesticides">{{cite web |url=http://www.fws.gov/pacific/ecoservices/envicon/pim/reports/Sacramento/SacramentoDelta.htm |title=Tissue Residues and Hazards of Waterborne Pesticides for Federally Listed and Candidate Fishes of the Sacramento-San Joaquin River Delta |publisher=U.S. Fish and Wildlife Service |year=2001 |access-date=August 16, 2013 |archive-date=May 26, 2014 |archive-url=https://web.archive.org/web/20140526060642/http://www.fws.gov/pacific/ecoservices/envicon/pim/reports/Sacramento/SacramentoDelta.htm |url-status=live }}</ref> A survey in 2012 recorded a spring duck population of 48.6 million, the highest since counts began in 1955.<ref>{{cite web |url = http://www.deltawaterfowl.org/media/pr/2012/120703-BPOP.php |title = Duck Populations Hit All-Time Record: Breeding Survey estimates 48.6 million ducks; Mallards at highest level since 1999 |publisher = Delta Waterfowl |year = 2012 |access-date = August 21, 2013 |url-status = dead |archive-url = https://web.archive.org/web/20121023065538/http://www.deltawaterfowl.org/media/pr/2012/120703-BPOP.php |archive-date = October 23, 2012 }}</ref> Large mammals in the Delta have not fared so well; with most of their habitat converted to agriculture, remaining populations were highly susceptible to human impacts and natural disasters. Grizzlies were hunted to extinction, while the flood of 1878 wiped out the last of the elk herds in the Delta.<ref name="legacies"/>
The Delta is home to approximately 22 species of fish, including several [[Pacific salmon]] species, [[striped bass]], [[steelhead trout]], [[American shad]] and [[sturgeon]].<ref name="DWR"/> About two-thirds of California's salmon pass through the Delta on their way upstream to spawn.<ref name="pesticides"/> The small [[Delta smelt]] is a key indicator species for the health of the Delta's ecosystem. Delta fish populations have been significantly reduced due to the reclamation of marshland and diversions of fresh water. In 2004, the Delta smelt was found to be on the edge of extinction.<ref name=clean>{{cite web |url = http://www.coastal.ca.gov/ccbn/keep_the_delta_clean.html |title = Keep the Delta Clean, Clean Boating Program |publisher = California Coastal Commission |access-date = August 20, 2012 |url-status = dead |archive-url = https://web.archive.org/web/20140720184633/http://www.coastal.ca.gov/ccbn/keep_the_delta_clean.html |archive-date = July 20, 2014 }}</ref> The survival of the Delta smelt has been one of the largest environmental issues in California, as environmental measures enacted to protect its population have often reduced the amount of water available for federal water projects that depend on water pumped from the Sacramento–San Joaquin Delta.<ref>{{cite news |url=http://www.kpbs.org/news/2013/feb/12/delta-smelt-deaths-means-less-water-central-and-so/ |title=Delta Smelt Deaths Means Less Water for Central and Southern California |work=KPBS |author=Quinton, Amy |date=February 12, 2013 |access-date=August 22, 2013 |archive-date=February 16, 2013 |archive-url=https://web.archive.org/web/20130216050644/http://www.kpbs.org/news/2013/feb/12/delta-smelt-deaths-means-less-water-central-and-so/ |url-status=live }}</ref>
The [[California Office of Environmental Health Hazard Assessment]] has issued a safe eating advisory for any fish caught in Central and South parts of the Delta due to elevated levels of mercury and PCBs. In addition, there is a notice of "DO NOT EAT" for any fish or shellfish from the [[Port of Stockton]].<ref>{{Cite web|url=https://oehha.ca.gov/fish/advisories/delta-central-and-south-0|title=Delta, Central and South|last=Admin|first=OEHHA|date=September 21, 2018|website=oehha.ca.gov|access-date=November 7, 2018|archive-date=February 23, 2019|archive-url=https://web.archive.org/web/20190223173249/https://oehha.ca.gov/fish/advisories/delta-central-and-south-0|url-status=live}}</ref> There is a separate safe eating advisory for the Northern part of the Delta. A 2010 study shows that the anglers in the Delta who ate these fish had higher levels of mercury in their system.<ref>{{Cite journal |last1=Shilling |first1=Fraser |last2=White |first2=Aubrey |last3=Lippert |first3=Lucas |last4=Lubell |first4=Mark |date=May 2010 |title=Contaminated fish consumption in California's Central Valley Delta |url=https://linkinghub.elsevier.com/retrieve/pii/S001393511000023X |journal=Environmental Research |language=en |volume=110 |issue=4 |pages=334–344 |doi=10.1016/j.envres.2010.02.002|pmid=20176346 |bibcode=2010ER....110..334S |url-access=subscription }}</ref> Delta fish have also been found to have high levels of a toxin called [[methylmercury]] which originates from old gold rush era mines in the Sierras. In that same study, it was found that women along the delta were consuming high numbers of fish, making them more susceptible to poisoning.<ref>{{Cite journal |last1=Silver |first1=Elana |last2=Kaslow |first2=Jessica |last3=Lee |first3=Diana |last4=Lee |first4=Sun |last5=Lynn Tan |first5=May |last6=Weis |first6=Erica |last7=Ujihara |first7=Alyce |date=July 2007 |title=Fish consumption and advisory awareness among low-income women in California's Sacramento–San Joaquin Delta |url=https://linkinghub.elsevier.com/retrieve/pii/S0013935107000552 |journal=Environmental Research |language=en |volume=104 |issue=3 |pages=410–419 |doi=10.1016/j.envres.2007.03.003|pmid=17459365 |bibcode=2007ER....104..410S |url-access=subscription }}</ref>
[[Nutria]] were found in Merced County in 2017 on the edge of the Delta. State officials are concerned that they will harm the infrastructure that sends water to San Joaquin Valley farms and urban areas.<ref>{{Cite news|url=https://www.latimes.com/local/lanow/la-me-ln-nutria-invasion-20190212-story.html|title=You think the rats at L.A. City Hall are bad? Officials have a $1.9-million plan to rid state marshlands of giant rodents|last=Fry|first=Hannah|date=February 16, 2019|newspaper=[[Los Angeles Times]]|access-date=February 16, 2019|archive-date=February 16, 2019|archive-url=https://web.archive.org/web/20190216181236/https://www.latimes.com/local/lanow/la-me-ln-nutria-invasion-20190212-story.html|url-status=live}}</ref>
The Delta has seen numerous [[cyanobacteria]] blooms with increasing frequency over the past two decades.<ref name="auto">Lehman, P.W., Marr, K., Boyer, G.L., Acuna, S., and Teh, S.J. (2013) Long-term trends and causal factors associated with Microcystis abundance and toxicity in San Francisco Estuary and implications for climate change impacts. Hydrobiologia 718: 141–158. {{doi|10.1007/s10750-013-1612-8}}</ref> Cyanobacteria have the potential to produce [[cyanotoxin]]s which can pose a risk to humans and animals upon contact.<ref name="auto1">Mankiewicz-Boczek, Joanna & WALTER, ZOFIA & Zalewski, Maciej & Konopnickiej, M.. (2002). Natural toxins from cyanobacteria. Acta Biol. Cracov Bot. 45. {{ISSN|0001-5296}}</ref> Because of this cyanobacteria blooms are seen as a threat that has the potential to impact human life. Several types of toxic cyanobacteria have appeared in the Delta, with ''[[Microcystis aeruginosa]]'' being one of the most common types.<ref name=":0" /> ''Microcystis aeruginosa'' produce [[microcystin]]s which are hepatotoxins that can cause liver cancer.<ref name="auto3">{{cite journal |last1=Zegura |first1=Bojana |last2=Sedmak |first2=Bojan |last3=Filipic |first3=Metka |date=2003 |title=Microcystin-LR induces oxidative DNA damage in human hepatoma cell line HepG2. |journal=[[Toxicon]] |volume=41 |pages=41–48 |doi=10.1016/S0041-0101(02)00207-6}}</ref> Frequent ''Microcystis'' blooms have impacted the food web of the Delta at multiple [[trophic level]]s. ''Microcystis spp.'' blooms in the Delta were found to decrease the [[Biodiversity|diversity]] of the aquatic microbial community.<ref name=":1">{{cite journal |last1=Otten |first1=T.G. |last2=Paerl |first2=H.W. |last3=Dreher |first3=T.W. |last4=Kimmerer |first4=W.J. and |last5=Parker |first5=A.E. |title=The molecular ecology of ''Microcystis'' sp. blooms in the San Francisco Estuary. |journal=[[Environmental Microbiology]] |volume=19 |pages=3619–3637 |date=20 July 2017 |doi=10.1111/1462-2920.13860}}</ref> Additionally, the cyanobacteria blooms in the Delta have led to decreased [[zooplankton]] [[mass]] and [[density]].<ref name="auto2">Stringfellow, William. (2013). Unprecedented Bloom of Toxin-Producing Cyanobacteria in the Southern Bay-Delta Estuary and its Potential Negative Impact on the Aquatic Food-Web (Report 4.5.1). {{doi|10.13140/RG.2.1.3730.3768}}.</ref> There is also concern for further spread throughout the food web via [[bioaccumulation]]. Microcystins were detected in the tissue of clams at levels much higher than the ambient water around them because of microcystin's ability to [[Covalent bond|covalently]] bind to tissue.<ref name=":2">Bolotaolo M, Kurobe T, Puschner B, et al. Analysis of Covalently Bound Microcystins in Sediments and Clam Tissue in the Sacramento-San Joaquin River Delta, California, USA. ''Toxins (Basel)''. 2020;12(3):178. Published 2020 Mar 13. {{doi|10.3390/toxins12030178|doi-access=free}}</ref>
The increased occurrences of cyanobacteria blooms in the Delta can be attributed to a variety of factors with the most important being lowered [[streamflow]].<ref name=":0" /> From 2004 through 2008 researchers collected different [[water quality]] parameters during the cyanobacteria blooms and determined that the blooms appeared after reaching a threshold of 19 °C (66 °F) which was exacerbated by reduced [[precipitation]], reduced streamflow, and increased [[Nutrient pollution|nutrient]] concentrations. They also determined that the negative attributes associated with [[climate change]] like reduced precipitation and increased temperatures could further increase the possibility of cyanobacteria blooms in the Delta. The high prevalence of nutrient concentrations in the Delta also plays a significant part in the increased frequency of ''Microcystis'' ''aeruginosa'' blooms.<ref>Mioni, Cecile & Kudela, Raphael & Baxa, Dolores. (2011). Harmful cyanobacteria blooms and their toxins in Clear Lake and the Sacramento-San Joaquin Delta (California). Report Prepared for Central Valley Regional Water Quality Control Board.</ref> ''Microcystis'' benefits greatly from anthropogenic inputs of nitrogen which allows it to out-compete other [[primary producer]]s and dominate the lower trophic levels.<ref name=":3">Noriko Takamura, Toshio Iwakuma, Masayuki Yasuno, Uptake of 13 C and 15 N (ammonium, nitrate and urea) by ''Microcystis'' in Lake Kasumigaura, ''Journal of Plankton Research'', Volume 9, Issue 1, 1987, Pages 151–165, {{doi|10.1093/plankt/9.1.151}}</ref> There have also been large amounts of nutrients monitored in the Delta as a result of various human activities.<ref>Kraus, T.E.C., Bergamaschi, B.A., and Downing, B.D., 2017, An introduction to high-frequency nutrient and biogeochemical monitoring for the Sacramento–San Joaquin Delta, northern California: U.S. Geological Survey Scientific Investigations Report 2017–5071, 41 p., {{doi|10.3133/sir20175071}} {{Cite web |url=https://pubs.er.usgs.gov/publication/sir20175071 |title=An introduction to high-frequency nutrient and biogeochemical monitoring for the Sacramento–San Joaquin Delta, northern California |access-date=June 16, 2021 |archive-date=June 16, 2021 |archive-url=https://web.archive.org/web/20210616125005/https://pubs.er.usgs.gov/publication/sir20175071 |url-status=bot: unknown }}</ref>
The increased presence of ''Microcystis aeruginosa'' blooms in the Delta represents a continual threat for species at multiple trophic levels. The lower trophic levels are affected from both reduced diversity as well as reduced numbers through competition.<ref name=":1" /><ref name=":3" /> When the conditions are met ''Microcystis'' have the ability to dominate the lower trophic levels hence why they are able to bloom.<ref name=":0" /> Additionally, when microcystins are present in the system then the consumers in the food web are at risk due to the effects of bioaccumulation.<ref name=":2" /> Fish that are present and active during cyanobacteria blooms can often have microcystin levels high enough to produce sublethal effects.<ref>Berg M and Sutula M. 2015. Factors affecting the growth of cyanobacteria with special emphasis on the Sacramento-San Joaquin Delta. Southern California Coastal Water Research Project, Technical Report 869 August 2015.</ref> Because microcystins can concentrate inside fish at multiple trophic levels it also represents a risk for human consumption as well.
==Conservation efforts== [[File:Delta water tower in Isleton, California - Sarah Stierch.jpg|thumbnail|right|180px|Water tower in Isleton, California]]
After numerous rounds of mitigation following the 2005 Smelt Biological Opinion (BiOp) lead to pumping restrictions from the State and Federal projects from the Delta, a number of potential solutions to the Delta's problems have been proposed. These followed the [[CALFED]] process which had offered several staged solutions. A first set of alternatives would maintain the Delta in its current condition and configuration. The second would restore parts of the Delta more closely to its natural state but include the construction of an additional Peripheral Canal to maintain the water supply currently provided by the Delta.<ref name="PPIC">{{cite web |url=http://www.ppic.org/content/pubs/rb/RB_207JLRB.pdf |title=Dealing with the Delta: Envisioning Futures, Finding Solutions |publisher=Public Policy Institute of California |work=Research Brief, Issue #114 |date=February 2007 |access-date=August 20, 2012 |archive-date=August 19, 2012 |archive-url=https://web.archive.org/web/20120819231750/http://www.ppic.org/content/pubs/rb/RB_207JLRB.pdf |url-status=live }}</ref>
[[File:Floating Robots in the Sacramento River Delta.jpg|thumb|left|180px|The launch of 100 floating sensors into the [[Sacramento River]] for the [[Floating Sensor Network project]]]] The Contra Costa County Public Works Department is working with the California Coastal Commission and the Department of Boating and Waterways to protect the drinking water quality, prevent pollution, and promote the environmental health of the Delta.<ref name=clean/>
In April 2009, the Sacramento River in the Delta was declared the nation's most endangered waterway system by the environmental group [[American Rivers (organization)|American Rivers]], due to water shortages caused by the Delta's environmental problems, declining fish populations and aging levees, among other problems.<ref>{{cite news |url = http://www.sacbee.com/topstories/story/1760320.html |title = Delta rivers top U.S. most-troubled list |work = Sacramento Bee |archive-url = https://web.archive.org/web/20090421132223/http://www.sacbee.com/reg-bin/tint.cgi?mode=denied%3Bgoto%3Dhttp%3A%2F%2Fweb.archive.org%2Fweb%2F20090412124355%2Fhttp%3A%2F%2Fwww.sacbee.com%2Ftopstories%2Fstory%2F1760320.html |archive-date = April 21, 2009 |date = April 2009 |access-date = August 21, 2013 |url-status = dead }}</ref>
Since the 1940s, various groups have lobbied for the construction of a [[Peripheral Canal]] to redirect water flowing from the Sacramento and San Joaquin rivers directly to the federal aqueducts that draw water from the southern end of the Delta.<ref>{{cite web |url = http://www.c-win.org/peripheral-canals-way-past-past-and-present.html |title = Peripheral Canals: Way Past, Past, and Present |publisher = California Water Impact Network |access-date = August 17, 2013 |url-status = dead |archive-url = https://web.archive.org/web/20130906205249/http://c-win.org/peripheral-canals-way-past-past-and-present.html |archive-date = September 6, 2013 }}</ref> Currently, freshwater entering the Delta has to flow through a maze of river channels and sloughs before entering the [[Clifton Court Forebay]] north of [[Tracy, California|Tracy]], where water is pumped into the [[California Aqueduct]] and [[Delta-Mendota Canal]].<ref>{{cite web |url=http://www.deltacollege.edu/org/deltawinds/DWOnline12/theperipheralcanal.html |title=The Peripheral Canal: What It Means for the Delta |author=Piazza, Tamara |publisher=San Joaquin Delta College |work=Delta Winds |year=2012 |access-date=August 17, 2013 |archive-date=March 14, 2013 |archive-url=https://web.archive.org/web/20130314040823/http://www.deltacollege.edu/org/deltawinds/DWOnline12/theperipheralcanal.html |url-status=live }}</ref> In addition, large numbers of Delta smelt and other endangered species are killed by the pumping plants that provide water for the aqueducts.<ref>{{cite web|url=http://blog.sfgate.com/opinionshop/2012/07/24/the-return-of-the-peripheral-canal/|title=The return of the peripheral canal|author=Kazakoff, Lois|date=July 24, 2012|work=The Opinion Shop|publisher=SFGate|access-date=August 17, 2013|archive-date=May 11, 2013|archive-url=https://web.archive.org/web/20130511233720/http://blog.sfgate.com/opinionshop/2012/07/24/the-return-of-the-peripheral-canal/|url-status=live}}</ref>
The current proposal, known as the [[Bay Delta Conservation Plan]], entails building twin tunnels under the delta and is closely associated with [[Governor of California|Governor]] [[Jerry Brown]]. However, the Peripheral Canal proposal has been criticized because it would further reduce the amount of freshwater flowing through the Delta. Farmers in the Delta are among the most opposed to the project because it would decrease the amount of water available to them for irrigation.<ref>{{cite news |url=https://www.latimes.com/opinion/la-xpm-2012-jun-25-la-oe-newton-column-peripheral-canal-brown-20120625-story.html |title=Newton: Water ethics and a peripheral canal – Southern California needs the water, and Northern California has it. But let's not sacrifice the delta. |work=Los Angeles Times |author=Newton, Jim |date=June 25, 2012 |access-date=August 21, 2013 |archive-date=August 17, 2013 |archive-url=https://web.archive.org/web/20130817090041/http://articles.latimes.com/2012/jun/25/opinion/la-oe-newton-column-peripheral-canal-brown-20120625 |url-status=live }}</ref>
All solutions, however, aim to produce a Delta which simultaneously supports a vibrant ecosystem and continues to supply fresh water to the Central Valley Project, the State Water Project and the Bay Area.<ref name="PPIC"/>
Sacramento–San Joaquin Delta National Heritage Area was designated on March 12, 2019, the first such designation for California, as part of the [[John D. Dingell Jr. Conservation, Management, and Recreation Act]].<ref>{{cite news |last1=Larson |first1=Elizabeth |title=President signs bill establishing Sacramento-San Joaquin Delta as California's first National Heritage Area |url=http://lakeconews.com/index.php/news/community/60377-president-signs-bill-establishing-sacramento-san-joaquin-delta-as-california-s-first-national-heritage-area |access-date=March 14, 2019 |work=Lake County News |date=March 13, 2019 |archive-date=August 5, 2020 |archive-url=https://web.archive.org/web/20200805143951/http://lakeconews.com/index.php/news/community/60377-president-signs-bill-establishing-sacramento-san-joaquin-delta-as-california-s-first-national-heritage-area |url-status=live }}</ref><ref>{{cite web |title=John D. Dingell, Jr. Conservation, Management, and Recreation Act |url=https://www.congress.gov/bill/116th-congress/senate-bill/47/text |website=congress.gov |access-date=March 14, 2019 |archive-date=March 18, 2019 |archive-url=https://web.archive.org/web/20190318170636/https://www.congress.gov/bill/116th-congress/senate-bill/47/text |url-status=live }}</ref> The Sacramento–San Joaquin Delta National Heritage Area is managed by the Delta Protection Commission.
==See also== {{Portal|California}} * [[Big Break Regional Shoreline]] * [[CALFED Bay-Delta Program]] * [[John P. Irish]], Delta landowner
== References == {{Reflist}}
==Works cited== *{{cite web |url=http://www.calwater.ca.gov/Admin_Record/C-073579.pdf |author=Pierce, Patricia |title=A Geoarchaeological Analysis of the Prehistoric Sacramento-San Joaquin Delta, California |publisher=Calfed Bay-Delta Program |date=June 1988 |access-date=August 20, 2013}} *{{cite book |author=Reisner, Marc |title=A Dangerous Place: California's Unsettling Fate |publisher=Penguin Books |year=2004 |isbn=0-679-42011-8 |url-access=registration |url=https://archive.org/details/dangerousplaceca00reis }} *{{cite web |url=http://ccrm.berkeley.edu/resin/pdfs_and_other_docs/background-lit/EarlyReclamationandAbandomentofDelta.pdf |author=Thompson, John |title=Early Reclamation and Abandonment of the Central Sacramento-San Joaquin Delta |publisher=University of California Berkeley |work=Sacramento History Journal |year=2006 |access-date=August 15, 2013 |archive-date=July 18, 2013 |archive-url=https://web.archive.org/web/20130718204252/http://ccrm.berkeley.edu/resin/pdfs_and_other_docs/background-lit/EarlyReclamationandAbandomentofDelta.pdf |url-status=dead }}
==Further reading== * {{cite book|title=Layperson's guide to the Delta|date=2010|publisher=Water Education Foundation}} * Gillenkirk, Jeff and Motlow, James. [http://www.bittermelonbook.com ''Bitter Melon: Inside America's Last Rural Chinese Town''] {{Webarchive|url=https://web.archive.org/web/20150416034514/http://www.bittermelonbook.com/ |date=April 16, 2015 }} (Nine Mile Press, 2015). Oral histories and photographs of residents of Locke, California in the Sacramento-San Joaquin Delta. * [https://escholarship.org/uc/jmie_sfews San Francisco Estuary and Watershed Science (online journal)]
==External links== {{Commons category|Sacramento–San Joaquin River Delta}} * [http://www.californiadelta.org/ California Delta Chambers and Visitors Bureau] * [http://deltaconservancy.ca.gov/ Sacramento-San Joaquin Delta Conservancy] * {{usurped|1=[https://web.archive.org/web/19961227014657/http://www.deltawetlands.com/ Delta Wetlands Project]}} * [http://baydeltaoffice.water.ca.gov/DeltaAtlas/ Sacramento-San Joaquin Delta Atlas] {{Webarchive|url=https://web.archive.org/web/20170616152007/http://baydeltaoffice.water.ca.gov/DeltaAtlas/ |date=June 16, 2017 }} at [[California Department of Water Resources]] * [http://baydelta.wordpress.com/2009/09/20/bay-delta-levees-climate-change-and-water-quality/ Bay-Delta: Levees, Climate Change, and Water Quality] * [http://www.mavensmanor.com/slideshows/Delta%20slideshow/Delta%20slideshow.swf What is this place called the Delta? (slideshow)] {{Webarchive|url=https://web.archive.org/web/20121211031327/http://www.mavensmanor.com/slideshows/Delta%20slideshow/Delta%20slideshow.swf |date=December 11, 2012 }} * [http://baydeltaoffice.water.ca.gov/DeltaAtlas/03-Waterways.pdf Delta Waterways] {{Webarchive|url=https://web.archive.org/web/20110708023140/http://baydeltaoffice.water.ca.gov/DeltaAtlas/03-Waterways.pdf |date=July 8, 2011 }} at [[California Department of Water Resources]] * [http://sfgate.com/cgi-bin/article.cgi?file=/c/a/2004/06/04/MNG1G70S3A1.DTL SFGate: Deluge in the Delta (4 Jun 2004)] {{Webarchive|url=https://web.archive.org/web/20091008002137/http://www.sfgate.com/cgi-bin/article.cgi?file=/c/a/2004/06/04/MNG1G70S3A1.DTL |date=October 8, 2009 }} * [http://news.cnet.com/Visiting-San-Francisco-Bay%2C-in-a-warehouse/2100-1041_3-6204642.html?tag=mncol;9n: Cnet – Visiting SF Bay (and delta) in a warehouse. Article by Daniel Terdimen, photos by James Martin, Cnet News, Aug 27, 2007] * [http://news.cnet.com/8301-30252_3-20000833-246.html?tag=mncol;3n: Cnet – Barge-scale cleanup in California waterways (photos), by James Martin, March 20, 2010] * [http://news.cnet.com/2300-11128_3-10002853.html?tag=mncol;4n: Cnet – Engineering a massive cleanup of toxic waterways (photos), by James Martin, March 20, 2010] * [http://www.oac.cdlib.org/findaid/ark:/13030/tf2199n8c6/ San Joaquin Delta Land Reclamation Photographs, ca. 1904–1907], [[The Bancroft Library]]
{{Coord|38.067975|-121.8427354|region:US-CA_source:gnis-1828941|display=title}}
{{Sacramento–San Joaquin Delta}} {{NatHerArea}} {{San Francisco Bay watershed}} {{Authority control}}
{{DEFAULTSORT:Sacramento-San Joaquin River Delta}} [[Category:Sacramento–San Joaquin River Delta| ]] [[Category:River deltas of the United States]] [[Category:Sacramento River|.Delta]] [[Category:San Joaquin River|.Delta]] [[Category:Estuaries of California]] [[Category:Geography of the Central Valley (California)|*•Delta]] [[Category:Geography of the San Joaquin Valley]] [[Category:Geography of the Sacramento Valley]] [[Category:Geography of the San Francisco Bay Area]] [[Category:Landforms of Contra Costa County, California]] [[Category:Landforms of Sacramento County, California]] [[Category:Landforms of Solano County, California]] [[Category:Landforms of San Joaquin County, California]] [[Category:Polders]] [[Category:Dikes in the United States]] [[Category:Regions of California]]