The clearest freshwater ever reported – Rotomairewhenua, New Zealand
Rotomairewhenua (or Blue Lake) is a small lake in Nelson Lakes National Park, in the northern reaches of New Zealand's Southern Alps. The lake has the clearest natural body of fresh water yet reported. A 2011 study found its visibility ranged from 70 to 80 metres (230 to 260 ft), clearer than the 63 metres (207 ft) measured for Te Waikoropupu Springs, a previous record holder. For comparison, laboratory measurements show distilled water has a visibility of approximately 80 metres (260 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 water's natural blue-violet colour. This research was funded by NIWA, and supported by the Department of Conservation. NIWA is currently planning future surveys with DOC approval to more thoroughly investigate the biodiversity of Blue Lake, the limnology of Lake Constance and the connections between the two.
Blue Lake lies within the rohe (tribal area) of Ngati Apa ki te Ra To. As part of the iwi's 2010 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 (sacred). Blue Lake was used only for males; Lake Constance was used for females. Its Maori name Rotomairewhenua means "the lake of peaceful lands".
Freshwater Ecoregion of the World : #811 New Zealand
Major Habitat Type: temperate coastal rivers
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Aerials and Landscapes
U21-506 Lake Constance
Aerials : On the way to Rotomairewhenua
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