Mitsuishi River (三石川) is a river in Hokkaido, Japan. It is 31.6 km in length and has a drainage area of 159.4 km2.

Course

The Mitsuishi River originates at Mount Setaushi (859 km) in the Hidaka Mountains and flows roughly south to southwest. The river flows into a reservoir at the Mitsuishi Dam. The Mitsuishi Dam was completed on the river in 1992 to prevent the flow of earth and sand from the Pirashike area (ピラシケ地区), which is prone to landslides. It then continues until it reaches the Pacific Ocean at Mitsuishi in Shinhidaka, Hokkaido.

Tributaries