The lake was made by an accident. Around twenty thousand years ago Mount Nantai erupted, lava ran down into the valley below, the valley was dammed, and the water that gathered behind it became Chuzenjiko—twenty-five kilometres around, a hundred and sixty-three metres deep, sitting at 1,269 metres above the sea. A path follows the shore, so the whole thing can be taken slowly and on foot, with Nantai standing over the water on the northern side.

It was a summer place first. From the Meiji era into the early Showa years foreign legations built their villas along this shore, coming up from the heat of the plain; the British and Italian embassy houses still stand and can be visited. People came here to be cool. The autumn crowds are a later habit.

The lake and the falls below it lie within Nikko National Park, and Kegon, which drains the lake over a 97-metre drop, is counted among Japan's best-known waterfalls.

There are two ways to look at it and they are not the same view. From the shore, with the mountain behind the water. Or from a sightseeing boat, which in season adds a route built around the colour and shows you the shoreline at an angle the road cannot reach. For the wider frame there is Hangetsuyama above the southern shore, where the Hatchoujima peninsula finally resolves into a shape. Buses from Tobu Nikko Station take about fifty minutes, and it is five minutes on foot from the stop to the water.