Lake Waiau

Lake in Hawaii, United States

Lake Waiau is a high elevation lake located at above sea level on Mauna Kea, on the island of Hawaiʻi. It is arguably one of the highest lakes in the United States. After the evaporation of Ka Wai o Pele in 2018 and the short lived lake in Halema'uma'u crater in 2020, Lake Waiau is the only lake on Hawaiʻi Island and one of very few lakes at all in the state of Hawaiʻi. It is relatively small, only about 100 m across, and varies in size as the water level rises and falls. At high water levels a small outlet stream appears at the northwest end, but it is absorbed into the ground after a short distance. The name means "swirling water" in Hawaiian, though it is usually rather placid. It usually freezes in winter, but aquatic insects such as midges and beetles can be found breeding in the water.

Lake Waiau is located inside the Pu'u Waiau cinder cone at an altitude of 3970 m. It is approximately heart shaped and its diameter reaches about 100 m. The average surface area of the lake is around The size of its surface area fluctuates significantly over the year. It reaches its peak during spring with a maximal depth between 2 m and 2.5 m. By the end of the summer, it often has shrunk to one third of its original size with a maximal depth below 1 m. A spillover into the Pohakuloa Gulch occurs when the lake depth is more than 2.3 m. The lake is only fed by precipitation, which occurs primarily during the winter; its catchment area is about , mostly located within the Pu'u Waiau cinder cone. The exact causes for the water loss are unknown. The suspects are drought conditions and the thawing of an assumed permafrost layer under the lake leading to increased seepage.