The Tennessee River rises from headwaters in the mountains of Tennessee, Virginia, North Carolina, and Georgia, and its main stream begins at Knoxville where the Holston and French Broad Rivers join. Its valley covers 41,000 square miles, receives an average of 52 inches of rain a year, and in water discharged into the Ohio and Mississippi is about equal in size to the Missouri. The Tennessee Valley Authority harnessed the river through a multi-purpose system of dams and reservoirs that regulates floods, improves navigation, generates electric power, and also helps protect the lower Ohio and Mississippi Valleys. High dams on tributaries create large storage reservoirs that hold back floodwaters and release them as needed to maintain downstream navigation depths while generating electricity. Nine main river dams with locks form a 650-mile navigation channel from Knoxville to the Ohio River, an important part of the nation’s inland waterway system connecting 20 states. After developing virtually all of the river’s power resources, TVA built huge coal-burning steam electric plants to help meet the region’s growing power needs. TVA sells power at wholesale to cities and rural electric cooperatives for retail distribution to homes, farms, businesses, and industry, while a few major industries and U.S. Government defense installations are served directly. The largest direct users, consuming more power than a great city, are the atomic plants at Oak Ridge, Tennessee, and Paducah, Kentucky. The TVA River Control System also supports steam plants by providing abundant cold water for condensing steam, and at Bull Run Steam Plant water is taken from Melton Hill Reservoir through the intake channel and returned to the reservoir after leaving the condensers.