Chuzenji (chōzānˈjē) [key], mountain lake, c.5 sq mi (13 sq km), Tochigi prefecture, central Honshu, Japan, in Nikko National Park. The lake is famed for its beauty. The Kegon waterfall (350 ft/107 m high) spills from the lake's outlet. On the shore stands the ancient Buddhist temple of Chuzenji. The lake is also called Satsu-no-umi [Sea of Happiness].