Lake Chūzenji, also called Sea of Happiness, is a scenic lake in Nikkō National Park in the city of Nikkō, Tochigi Prefecture, Japan. It was created 20,000 years ago when Mount Nantai (2484 m) erupted and blocked the river.
The lake has a surface area of 11.62 km² and a circumference of 25 km. Its elevation at the surface is 1,269 m (4,124 ft), and the water reaches a depth of 163 m (508 ft).
The Yukawa River is the principal source of water.
It drains through the Kegon Falls.
