What is the main river in Japan?

The main river in Japan is the Shinano River. It is the longest river in the country, and it flows for 228 miles from Mount Kobushi to the Sea of Japan.

The Shinano River is so lengthy that it drains throughout most of the Japanese prefectures of Nagano and Niigata. At the lower reaches of the river's drainage, flooding used to be a major problem, which led to the construction of a discharge canal at Ozuku in 1923. The river is a key inland waterway in Japan, with Niigata and other river ports offering a valuable service to the Japanese economy.