Teshio River

The Teshio River is a river in Hokkaidō, Japan. At 256 kilometres, it is the second-longest river on the island and the fourth-longest in the country. A Class A river, the Teshio is the northernmost major river in Japan, and has been designated Hokkaidō Heritage. Matsuura Takeshirō is said to have come up with the name "Hokkaidō" during his exploration of the river's interior.

Source: Wikipedia