The Tongue River Reservoir State Park is a Montana state park. The 12 mile long reservoir

Reservoir

A reservoir , artificial lake or dam is used to store water.Reservoirs may be created in river valleys by the construction of a dam or may be built by excavation in the ground or by conventional construction techniques such as brickwork or cast concrete.The term reservoir may also be used to...

 is located 6 miles north of Decker, Montana

Decker, Montana

Decker is an unincorporated community in Big Horn County, Montana, United States. Decker is located along Secondary Highway 314 north-northeast of Sheridan. Decker has a post office with ZIP code 59025. The community is home to a one-room public school, the Spring Creek School; it has nine pupils...

. It is fed from Tongue River

Tongue River (Montana)

The Tongue River is a tributary of the Yellowstone River, approximately 265 mi long, in the U.S. states of Wyoming and Montana. The Tongue rises in Wyoming in the Big Horn Mountains, flows through northern Wyoming and southeastern Montana and empties into the Yellowstone River at Miles City,...

. The park occupies 642 acres at an elevation of 3468 feet.

Recreation includes boating, fishing and wildlife viewing. While the lake is open year round, the marina is only open from May to September.