Record #00488Nature archive
Rotomairewhenua (Blue Lake) in New Zealand's Nelson Lakes National Park reached 81.4 m of horizontal underwater visibility in measurements made during 2010–2011, the highest reported for natural freshwater.
Current Record
81.4m
Current record value
During six field visits in 2010–2011 researchers used an underwater black disk, measuring lines and viewing equipment to assess optical clarity. Horizontal visibility stayed above 70 m and reached 81.4 m at its clearest.
The lake is supplied by groundwater filtered through gravel and landslide debris from nearby Lake Constance, removing fine particles and coloured organic matter. The lake is culturally important to Ngāti Apa ki te Rā Tō, and conservation guidance asks visitors not to swim or wash in it.
The record conclusion has sufficient verification support.
Basis: direct confirmation by an authority
NIWA and the 2013 peer-reviewed optical paper support Blue Lake as the clearest reported freshwater with peak horizontal visibility of 81.4 m across six 2010–2011 visits. The precise date of the peak is unknown. WGS84 coordinates refer to the lake's representative point in a LINZ-derived NZTopo50 index, not a nearby hut.
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