The Big River is a tributary of the Meramec River in east-central Missouri. The river rises in western Iron County, near the summit of Johnson Mountain and the locale of Enough; it flows through Washington County, Saint Francois County, and Jefferson County. It forms part of the boundary between Jefferson County and Saint Francois County and also part of the boundary between Jefferson County and Washington County. It empties into the Meramec River, opposite Eureka, where the Meramec forms the border between Jefferson County and Saint Louis County. The river flows through Washington State Park, St. Francois State Park, and the Lead Belt mining district. The elevation of the river at its source is approximately 1,300 feet (400 m) above sea level and at its mouth about 400 feet (120 m). The length of the river is approximately 142 miles (229 km), while the airline distance between source and mouth is about 56 miles (90 km). Its watershed area is 955 square miles (2,470 km2). The river flows though the communities of Belgrade, Caledonia, Irondale, Park Hills, Bonne Terre, Morse Mill, Cedar Hill, Byrnesville, and Byrnes Mill. Tributaries of Big River include Flat River, Belew Creek, Turkey Creek, Mill Creek, Mineral Fork, Calico Creek, Dulin Creek, and Jones Creek. About 83 miles (134 km) are navigable; however, the remains of five small mill dams makes portage necessary, due to drops of several feet or high turbulence. Otherwise, the river is gentle for canoeing, with a Class I difficulty rating. Public parks are adjacent to most of these dams, and are popular fishing spots. Due to steady infeed of springwater, this river is navigable in all seasons. Major gamefish commonly found in the river include Largemouth bass, Smallmouth bass, Spotted bass, Rock bass, Longear sunfish, Bluegill, Channel catfish, Flathead catfish, and Redhorse suckers.