Located in the New Zealand national park, the Blue Lake, also known as Rotomairewhenua, holds the title of the world’s clearest lake. Scientific tests carried out in 2011 by New Zealand’s National Institute of Water and Atmospheric Research (NIWA) showed Blue Lake to be the clearest natural body of fresh water known to man. According to the results, visibility in the lake is up to 80 metres, which means the water is considered almost as ‘optically clear’ as distilled water. These clear waters are regarded by the local Maori iwi / tribe as tapu or sacred which means that humans are not permitted to enter the lake.