Ohio River course forms the northern borders of West Virginia and Kentucky; and the southern borders of Ohio, Indiana and Illinois, until it joins the Mississippi River at the city of Cairo, Illinois. Where the Ohio joins the Mississippi is the lowest elevation in the state of Illinois, at . The Ohio River, which flows westward from Pittsburgh, Pennsylvania, to Cairo, Illinois, is the largest tributary, by volume, of the Mississippi River in the United States. At the confluence, the Ohio is considerably bigger than the Mississippi. Measured by long-term mean discharge in cubic feet per second and cubic meters per second,
Big Black River (Mississippi) northern border of Claiborne County. The Big Black River and most of its tributaries are silt-filled. The rivers carry large amounts of suspended sediment, resulting mostly from agricultural runoff. These tributaries are slow-flowing muddy streams. However, some are swift-flowing with sandy bottoms. The Battle of Big Black River Bridge, fought during the Battle of Vicksburg, was part of the Vicksburg Campaign in the American Civil War. The size of the Big Black River Basin drainage area is . Its elevation varies from 50 to 650 feet (14 to 198 meters) above sea level. It is long and averages 22 to