Lake Waiau is a high-elevation lake located at 3,970 m (13,020 ft) above sea level on Mauna Kea, on the island of Hawaiʻi. It is arguably one of the highest lakes in the USA, 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.