is a nearly circular caldera lake in Shiraoi, Hokkaidà Â, Japan. It is part of Shikotsu-Tà Âya National Park. The lake is recognized as having the best water quality in all of Japan. With a transparency of , the lake ranks second to Lake Mashà « according to the Ministry of the Environment.
Resident species of the lake include a salamander species, . Since 1909, sockeye salmon have been introduced to the lake.