The Ohio River is a 981-mile long river in the United States. It is located at the boundary of the Midwestern and Southern United States, flowing southwesterly from far-western Pennsylvania south of Lake Erie to its mouth on the Mississippi River at the southern tip of Illinois. It is the third largest river by discharge volume in the United States and the largest tributary by volume of the north-south flowing Mississippi River that divides the eastern from western United States. The river flows through or along the border of six states, and its drainage basin includes parts of 14 states. Through its largest tributary, the Tennessee River, the basin includes several states of the southeastern U.S. It is the source of drinking water for three million people.
The lower Ohio River just below Louisville is obstructed by rapids known as the Falls of the Ohio where the water level falls 26 feet in 2 miles and is impassable for navigation. Completion of the McAlpine Locks and Dam, a shipping canal bypassing the rapids, allows commercial navigation from the Forks of the Ohio at Pittsburgh to the Port of New Orleans at the mouth of the Mississippi on the Gulf of Mexico.