Nelson's Blue Lake has been declared the clearest freshwater ever reported. Research by Niwa scientists reveal that the lake, in the Nelson Lakes National Park, has even greater visual clarity than that of the famed Te Waikoropupu Springs in nearby Golden Bay.

Niwa said its clarity was exceeded worldwide perhaps only by certain ocean waters, such as those in the Pacific near Easter Island. An expert team - after six helicopter visits - established the clarity to be from 70m to 80m, further than the 63m of Waikoropupu.