The Ohio River begins at the confluence of the Allegheny and Monongahela rivers in Pittsburgh, Pennsylvania, and flows 981 miles southwest to Cairo, Illinois, where it joins the Mississippi River. Henderson, Kentucky, is located at mile 804. Twenty-one dams along the river ensure that a minimum navigable channel nine feet deep is maintained year-round. The river averages a quarter mile in width and twenty-four feet in depth. Every year, 230 million tons of cargo are transported on the Ohio River, and approximately 70% of that cargo is coal and related energy products bound for the many power plants in the Ohio River basin.