
Get on the water in a boat at least once.
Rivers here are short, fast and clear, and the interesting thing is how many of them you can travel on. Flat wooden boats poled by a boatman, small craft you row yourself, and rapids run in a wooden hull are all ordinary tourist activities, priced in the low thousands of yen.
The Shimanto in Kochi is the one people mean by “the last clear river” — no large dam on its main course, crossed by low bridges built without railings so that floodwater passes over them rather than sweeping them away.
Boats depend on the water. Too little and they do not run; too much and they certainly do not. The decision is made on the morning, and it is not negotiable.
Book the day before for the popular ones, and ask about the water level in the same call.
It is colder on water, and several of these run through gorges in shade.
Life jackets are provided and worn. Wear it properly — the boatmen will check.
Each links to its prefecture.

The last clear river in Japan, with low railless bridges. Cycle it or go down it.

A gorge travelled by flat boat, poled by a boatman who sings on the way back.

A town of canals, travelled by punt through the middle of it.

A columned gorge you row into yourself, to the foot of a waterfall.

Shallow rapids in a wooden boat, and a gorge floor of flat rock to walk on.
One of the fastest rivers in Japan, and run by boat through the gorge.