Tennessee, river, c.650 mi (1,050 km) long, the principal tributary of the Ohio River. It is formed by the confluence of the Holston and French Broad rivers near Knoxville, Tenn., and follows a U-shaped course to enter the Ohio River at Paducah, Ky. Its drainage basin covers c.41,000 sq mi (106,200 sq km) and includes parts of seven states. Navigation was long impeded by variations in channel depths and by rapids, such as Muscle Shoals. However, the Tennessee Valley Authority (est. 1933) has converted the river into a chain of lakes held back by nine major dams (Kentucky, Pickwick Landing, Wilson, Wheeler, Guntersville, Nickajack, Chickamauga, Watts Bar, and Fort Loudoun). As a result of these improvements, river traffic increased; flooding was controlled; a water-oriented recreation industry was established; and hydroelectric power generated at the dams attracted new industries to the region. The Tennessee-Tombigbee Waterway, opened in 1985, links the Tennessee with the Gulf of Mexico by way of the Tombigbee and Mobile rivers. During the Civil War, the Tennessee River was a prime approach for a Union invasion of the South; several great battles were fought there (see Fort Henry; Shiloh, battle of; Chattanooga campaign).