| Mitsuishi River | |
| Name Other: | 三石川 |
| Subdivision Type1: | Country |
| Subdivision Name1: | Japan |
| Subdivision Type2: | State |
| Subdivision Name2: | Hokkaido |
| Subdivision Type3: | Region |
| Subdivision Name3: | Hidaka |
| Subdivision Type4: | District |
| Subdivision Name4: | Hidaka |
| Subdivision Type5: | Municipality |
| Subdivision Name5: | Shinhidaka |
| Length: | 31.6km (19.6miles) |
| Source1: | Mount Setaushi, Hidaka Mountains |
| Source1 Location: | Shinhidaka, Hokkaido, Japan |
| Source1 Coordinates: | 42.4214°N 142.6917°W |
| Source1 Elevation: | 280m (920feet) |
| Mouth: | Pacific Ocean |
| Mouth Location: | Shinhidaka, Hokkaido, Japan |
| Mouth Coordinates: | 42.2444°N 142.5697°W |
| Mouth Elevation: | 0m (00feet) |
| Basin Size: | 159.4km2 |
is a river in Hokkaido, Japan. It is 31.6km (19.6miles) in length and has a drainage area of 159.4km2.[1]
The Mitsuishi River originates at Mount Setaushi (859km (534miles))[1] 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, which is prone to landslides.[1] It then continues until it reaches the Pacific Ocean at Mitsuishi in Shinhidaka, Hokkaido.[2]