Rivers of Japan are characterized by their relatively short lengths and considerably steep gradients due to the narrow and mountainous topography of the country. An often-cited quote is 'this is not a river, but a waterfall' by the Dutch engineer (o-yatoi gaikokujin) Johannis de Rijke who had visited the Jōganji River, Toyama Prefecture. The Mogami, the Fuji and the Kuma are regarded as the three most rapid rivers of Japan.
Typical rivers of Japan rise from mountainous forests and cut out deep V-shaped valleys in their upper reaches, and form alluvial plains in their lower reaches which enable the Japanese to cultivate rice fields and to set up cities. Most rivers are dammed to supply both water and electricity.
The longest river of Japan is the Shinano, which flows from Nagano to Niigata. The Tone has the largest watershed and serves water to more than 30 million inhabitants of Tokyo metropolitan area.