Tongue River Reservoir State Park is a Montana state park on the western shore of Tongue River Reservoir, about 6 miles north of Decker. Covering 642 acres at an elevation of 3,468 feet, it centers on a 12-mile-long reservoir created by impounding the Tongue River. The park serves as a public recreation area for boating, fishing, camping, swimming, wildlife viewing, and access to a seasonal marina. Fishing is especially important on the reservoir’s 3,600 acres, which are regularly stocked and managed with emphasis on crappie, smallmouth bass, northern pike, and walleye. It remains a significant outdoor destination in southeastern Montana.