As of 2026, Lake Rotomairewhenua (Blue Lake) in New Zealand’s Nelson Lakes National Park holds the official title for the clearest freshwater body on Earth. Scientific studies validated by NIWA show that underwater visibility in the lake can reach up to 80 meters, which is remarkably close to the theoretical visibility of pure distilled water. The water is filtered through underground rock from the nearby Lake Constance, removing almost all suspended particles. Because the lake is considered "Tapu" (sacred) by the local Māori, swimming and any form of water entry are strictly prohibited to maintain this purity. In 2026, conservationists monitor the lake closely for "lake snow" (invasive algae), and visitors are asked to stay on designated boardwalks to ensure that the water remains a vivid, near-transparent violet-blue for future generations.