Lake Chūzenji was created by the eruption of Mt. Nantai 20,000 years ago. It has 11.90 km² wide area and 25 kilometers long circumference. It is the broadest lake in Tochigi Prefecture. Moreover, it is more than four kilometers wide with  the highest altitude except for artificial lakes. Water flows into the lake from Yugawa to Kegon Falls through Ōjili River. 