{{Short description|Lake in New Zealand}} {{Use dmy dates|date=January 2024}} {{Use New Zealand English|date=January 2024}} {{Infobox body of water | name = Rotomairewhenua | other_name = Blue Lake | image = Blue lake Nelson New Zealand.jpg | alt = Blue lake | caption = Blue lake | image_bathymetry = | caption_bathymetry = | location = [[Tasman Region]], [[South Island]] | mapframe = yes | mapframe-zoom = 12 | pushpin_map = New Zealand South Island | pushpin_map_alt = Location of Blue Lake | coords = {{coord|42|3|30.6|S|172|39|25.6|E|type:waterbody_region:NZ|display=inline,title}} | type = | inflow = [[Spring (hydrology)|springs]]<ref name=Gall>{{cite journal |last1=Gall |first1=Mark P. |last2=Davies-Colley |first2=Rob J. |last3=Merrilees |first3=Rob A. |year=2013 |title=Exceptional visual clarity and optical purity in a sub-alpine lake |journal=Limnology and Oceanography |volume=58 |issue=2 |pages=443–451 |doi=10.4319/lo.2013.58.2.0443 |doi-access=free}}</ref> | outflow = West Branch of the [[Sabine River, New Zealand|Sabine River]] | catchment = | basin_countries = New Zealand | length = | width = | area = {{convert|2.45|ha|acre|abbr=on}}<ref name=Gall /> | depth = {{convert|7|m|ft|abbr=on}}<ref name=Gall /> | max-depth = {{convert|8.5|m|ft|abbr=on}}<ref name=Gall /> | volume = {{convert|180000|m3|abbr=on}}<ref name=Gall /> | residence_time = <24 hours<ref name=Gall /> | shore = | elevation = {{convert|1180|m|ft|abbr=on}}<ref name=Gall /> | islands = | cities = }} '''Rotomairewhenua / Blue Lake''' is a small [[lake]] in [[Nelson Lakes National Park]], in the northern reaches of [[New Zealand]]'s [[Southern Alps (New Zealand)|Southern Alps]]. Sacred to local [[Māori people|Māori]], it has the clearest natural fresh water in the world.
==Description== [[File:Rotomairewhenua.jpg|alt=Rotomairewhenua from above the blue and green algae is distinctive|thumb|left|The algae and plant life in the lake make it look blue and green]]
The Blue Lake is drained by the west branch of the [[Sabine River, New Zealand|Sabine River]], which is part of the [[Buller River]] system. It is fed by a short upper segment of the Sabine, which in turn is fed by underground seepage through the landslide debris impounding the much larger [[Lake Constance, New Zealand|Lake Constance]]. Blue Lake is roughly boomerang shaped, running north then northwest, with each arm of the lake stretching some {{convert|200|m|ft|-2}}.<ref>{{cite web|title=Blue Lake|url=http://maps.google.co.nz/maps/ms?ie=UTF8&t=m&vpsrc=6&source=embed&oe=UTF8&msa=0&msid=200785319996428123531.0004b477c51e07b783a44|work=Google Maps|accessdate=24 December 2011}}</ref> Its waters are cold, ranging from {{convert|5|to|8|C|F}}.<ref name="NIWA"/>
===Clarity===
The lake has extremely clear water, and is the clearest natural body of fresh water yet reported.<ref name="NIWA"/><ref>{{cite news|title=Nelson's Blue Lake clearest|url=http://www.nzherald.co.nz/nz/news/article.cfm?c_id=1&objectid=10774272|accessdate=20 December 2011|newspaper=New Zealand Herald|date=20 December 2011}}</ref> A 2011 study found its [[water clarity|visibility]] ranged from {{convert|70|to|80|m|ft}}, clearer than the {{convert|63|m|ft}} measured for [[Te Waikoropupu Springs]], a previous record holder. For comparison, laboratory measurements show [[distilled water]] has a visibility of approximately {{convert|80|m|ft}}. Scientists attribute the lake water's clarity to its passage underground from Lake Constance, which filters out nearly all the particles suspended in the water. Its clarity reveals [[color of water|water's natural blue-violet colour]].<ref name="NIWA">{{cite web|title=Nelson's Blue Lake – The clearest freshwater ever reported|url=http://www.niwa.co.nz/news/nelson%E2%80%99s-blue-lake-%E2%80%93-the-clearest-freshwater-ever-reported|publisher=NIWA|accessdate=20 December 2011}}</ref>
==Facilities and access==
Blue Lake is most often reached as a side trip from the [[Travers-Sabine Circuit]], although a marked route to the south, over the [[Waiau Pass]] and another to the West, via [[Moss Pass]] continues beyond the lake. The nearby Blue Lake Hut, with 16 bunks, provides accommodation for more than 700 [[tramper]]s each year.<ref name="NIWA"/><ref name=DOC>{{cite web |title=Blue Lake Hut |url=https://www.doc.govt.nz/parks-and-recreation/places-to-go/nelson-tasman/places/nelson-lakes-national-park/things-to-do/huts/blue-lake-hut/ |publisher=Department of Conservation |accessdate=31 August 2021}}</ref>
==Māori history==
Blue Lake lies within the [[rohe]] (tribal area) of [[Ngāti Apa ki te Rā Tō]]. As part of the [[iwi]]'s 2010 [[Treaty of Waitangi claims and settlements|treaty settlement]], the lake passed into tribal ownership and was then given back to the Crown. The lake was traditionally used in ceremonies to cleanse the bones and release the spirits of the dead, so they could begin their journey to [[Hawaiki]], and the iwi regard its waters as [[Tapu (Polynesian culture)|tapu]] (sacred). (Blue Lake was used only for males; Lake Constance was used for females.) Its Māori name, ''Rotomairewhenua'', means "the lake of peaceful lands".<ref name=DOC/>
In August 2014, the official name for Blue Lake was altered to Rotomairewhenua / Blue Lake, following the Ngāti Apa ki te Rā Tō treaty settlement with the Crown.<ref>{{cite web|url=http://www.linz.govt.nz/regulatory/place-names/recent-place-name-decisions-and-place-names-interest/nzgb-decisions-august |title=NZGB decisions – August 2014 |date=August 2014 |website= |publisher=Land Information New Zealand |accessdate=27 October 2015 |url-status=dead |archive-url=https://web.archive.org/web/20151121203027/http://www.linz.govt.nz/regulatory/place-names/recent-place-name-decisions-and-place-names-interest/nzgb-decisions-august |archive-date=21 November 2015 }}</ref>
==References== {{Reflist}}
{{Nelson Lakes National Park}} {{Tasman District}}
[[Category:Lakes of the Tasman District]] [[Category:Sacred lakes]] [[Category:Nelson Lakes National Park]]