The Ohio River drains America's Heartland, stretching more than 981 miles from Pittsburgh, Pennsylvania to Cairo, Illinois where it joins the Mississippi River. Its 204,000 square mile watershed stretches north to south from New York to Alabama and east to west from Pennsylvania to Illinois. 14 major tributaries and 11 minor tributaries supply the river. Flows at its outlet range from 15,000 cubic feet per second to 1.85 million cubic feet per second (3 orders of magnitude and nearly 9 times the flow over Niagara Falls). There are 78 multi-purpose reservoirs. In addition, there are 31 projects that are operated by the Tennessee Valley Authority (TVA). The projects are maintained and operated by five districts, with the Great Lakes and Ohio River Division having oversight and operational Ohio/Mississippi River flood control responsibilities. Even with all these structures only approximately 1/3 of the Ohio River Basin runoff is controlled.