At night, the river is turned down.

Oirase is the only stream that leaves Lake Towada, and where it leaves there is a sluice gate. During the day the gate is open and water runs. At night, and through the winter, it is nearly closed.

The water you see in daylight is released for the sake of the view. Most of the lake's outflow is diverted through a tunnel to a power station; a fixed share is held back and sent down the gorge instead, under an arrangement settled in the 1930s and kept ever since. It is an odd thing to know while standing in front of a waterfall — that someone decided how much of it there would be.

The gradient helps too. The riverbed drops about one meter for every seventy it travels, which is almost flat. Slow water does not scour. Moss holds on the rocks and on the fallen trunks lying in midstream, and small shrubs root in places a faster river would have swept clean years ago.

Fourteen kilometers from the lake down to Yakeyama, with a road and a footpath running side by side the whole way. You can join it anywhere and leave it anywhere. Toward the end of October the maples and beeches come down over all of it.