Lake Chūzenji (中禅寺湖, Chūzenji-ko) 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 is the principal source of water. It drains through the Kegon Falls.
Chuzenjiko' shores are mostly undeveloped and forested except at the lake's eastern end where the small hot spring town of Chuzenjiko Onsen was built. The town is also the site of Kegon Waterfall, the most famous of several waterfalls in Nikko National Park. Another popular waterfall, Ryuzu Waterfall , is located at the northern shores of Lake Chuzenji where Yukawa River discharges into the lake.
Chuzenjiko is especially beautiful in mid to late October, when the autumn colors reach their peak along the lake's shores and surrounding mountains. And during Japan's hot summers, the lake's high elevation (1269 meters above sea level) keeps the area cool and comfortable, which in the past has attracted foreign embassies to build recreation villas along its shores.
It is possible to hike around the entire 25 kilometer circumference of Lake Chuzenji via hilly lakeside walking trails. Alternatively, the lake can be enjoyed from sightseeing boats that depart from Chuzenjiko Onsen. Panoramic views from above are possible from along the Chuzenjiko Skyline, an eight kilometer long former toll road which can now be used free of charge.