| Tongue River Reservoir | |
| Pushpin Map: | USA Montana |
| Coords: | 45.0606°N -106.79°W |
| Lake Type: | Reservoir |
| Inflow: | Tongue River |
| Outflow: | Tongue River |
| Basin Countries: | United States |
| Location: | Big Horn County, Montana |
| Elevation: | 4222feet |
The Tongue River Dam is a dam in Big Horn County, Montana, a few miles north of the Wyoming state border. It impounds the Tongue River, creating the Tongue River Reservoir.
The earthen dam was constructed in the river canyon in 1939, with a height of and a length at its crest of . It impounds Montana's north-flowing Tongue River for flood control and irrigation water storage. The dam and reservoir are owned and operated by the Montana Department of Natural Resources and Conservation.
The 12adj=midNaNadj=mid riverine reservoir it creates has a normal water surface of, a maximum capacity of, and normal storage of . Recreation includes boating, fishing for bass, crappie, walleye and northern pike, and camping in the Tongue River Reservoir State Park. For white-water rafters, the Tongue is a Class I river from the Dam downstream (northward) to its confluence with the Yellowstone River.