Cumberland River, a major river in the southeastern United States. From its source in the Cumberland Mountains of Kentucky, the river flows southwestward into Tennessee, then back into Kentucky, where it empties into the Ohio River at Smithland. The length of the river is 687 miles (1,106 km). Numerous dams have been built by the U.S. Corps of Engineers on the river and its tributaries. With their reservoirs and locks, the dams improve navigation, provide hydroelectric power and recreational facilities, and aid flood control. The largest reservoir is Lake Barkley, which adjoins Land Between the Lakes, a large recreational area in Kentucky and Tennessee. Near Corbin, Kentucky, the river drops 68 feet (21 m) at Cumberland Falls.