OHIO RIVER, the major eastern tributary of the Mississippi River, is also a significant river artery in the north central United States, extending for 981 miles from Pittsburgh, Pennsylvania, to Cairo, Illinois. Formed by the confluence of the Allegheny and Monongahela rivers (325 and almost 130 miles in length, respectively), at the Forks of the Ohio, the river flows northwest from the Keystone State before turning southwest and joining the Mississippi River at Cairo. At Pittsburgh the Ohio is 1,021 feet above sea level, and 322 feet at Cairo. The Falls of the Ohio at Louisville, Kentucky, is a 2.2-mile-long limestone rapids where the river drops 23.9 feet. Canalization around the rapids was completed in 1830, ensuring navigability. Between Pittsburgh and Wheeling, West
Virginia, the river averages 0.5 miles in width; between Cincinnati, Ohio, and Louisville, 1.1 miles; and from Louisville to Cairo, 1.3 miles.
The Ohio River and its valley have a complex geological history but are young, formed at the end of the Pleistocene epoch, about ten thousand years ago. The valley is narrow and characterized by steep bluffs, and the drainage basin includes about 203,900 square miles and has an annual average flow of 281,000 cubic feet per second. Six major tributaries join the Ohio from the north: the Wabash (Illinois-Indiana border); Muskingum, Miami, Hocking, and Scioto (Ohio); and Beaver (Pennsylvania). From the south the major tributaries are the Great Kanawha and Guyandotte (West Virginia); Big Sandy (West Virginia–Kentucky border); and Licking, Kentucky, Salt, Green, Cumberland, and Tennessee (Kentucky). About 80 percent of the state of Ohio and 85 percent of Kentucky drain into the Ohio-Mississippi system, and there are over 2,900 miles of navigable rivers in the ten-state area of the Ohio River system.
Politically the Ohio River marks the boundaries of five states: Ohio and West Virginia, Ohio and Kentucky, Indiana and Kentucky, and Illinois and Kentucky. In addition to Pittsburgh, the banks of the Ohio serve as the site of five major cities in Ohio (Cincinnati, Gallipolis, Marietta, Portsmouth, and Steubenville); four in Indiana (Madison, New Albany, Evansville, and Mount Vernon); three in West Virginia (Parkersburg, Huntington, and Wheeling); and five in Kentucky (Ashland, Covington, Louisville, Owensboro, and Paducah).
Banta, Richard E. The Ohio. Rivers of America Series 39. New York: Rinehart, 1949; reprinted Lexington: University Press of Kentucky, 1998.
Klein, Benjamin F., and Eleanor Klein, eds. The Ohio River Handbook and Picture Album. Cincinnati: Young and Klein, 1969.