(Japanese: Ishikari River), river, in Hokkaido, Japan, rising near the centre of the Kitami-sammyaku (Kitami Mountains). It flows for 120 mi (200 km) southwest in a broad arc, draining the Kamikawa-bonchi (Kamikawa Basin), the Sorachi-gawa (Sorachi River) lowland, and the Ishikari-heiya (Ishikari Plain). The river empties into Ishikari-wan (Ishikari Bay) of the Sea of Japan. Its name is derived from the Ainu term ishikaribetsu (“greatly meandering river”), which describes the flow of its lower course. Inundations usually occur twice a year, after the thaw of spring and the rains of summer. An extensive flood control project, providing a dependable water supply for heavy industries, has induced serious water pollution in the river valley, which was sacred to the Ainu.