Tiber Dam and its reservoir, Lake Elwell, are on the Marias River in north-central Montana. The dam and reservoir are features of the Lower Marias Unit of the Pick-Sloan Missouri Basin Project. The reservoir has 21,300 water surface acres, 21,244 land acres and 181 miles of shoreline. Major game fish include northern pike, walleye, and rainbow trout. Concrete boat ramps, campgrounds, marina, picnic shelters.