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Ohio River
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Ohio River

The Ohio River is a principal tributary of the Mississippi River, 981 mi (1,579 km) long in the eastern United States. Of great significance in the history of North America dating from the time of the Native Americans, the river was a primary transportation route during the westward expansion of the early U.S. It flows through or along the border of six states, and its watershed encompasses 13 states, including many of the states of the southeastern U.S. through its largest tributary, the Tennessee. During the eighteenth century it was the southern boundary of the Northwest Territory, thus serving as the border between free and slave territory.

Table of contents
1 Description
2 Pre-History
3 History
4 Cities along the Ohio


The river is formed by the confluence of the Allegheny and Monongahela rivers in downtown Pittsburgh. It flows west through western Pennsylvania, then SSW and SW, forming the border between West Virginia and Ohio, then between Kentucky and Ohio, Indiana, and Illinois. It joins the Mississippi from the east at Cairo, Illinois.

Major tributaries of the river, indicated by the location of their mouth, include:


The Ohio River was formed by glacial meltwater from the last ice age, the Wisconsin glaciation. During the glacial retreat, the river was temporarily dammed just southwest of Louisville, Kentucky, creating a large lake until the dam burst. The Ohio River largely supplanted the former Teays River drainage system, which was disrupted by the glaciers.


Since it was considered by pre-Columbian inhabitants of eastern North America to be part of a single river continuing on through the lower Mississippi, it is perhaps an understatement to characterize the Ohio as a mere tributary of the Mississippi. The river is 981 miles (1579 km) long and carries the largest volume of water of any upper tributary of the Mississippi. In fact, the Ohio typically carries a much greater volume of water than the upper Mississippi.

On May 19, 1749 King George II of Great Britain granted the Ohio Company a charter of land around the forks of the Ohio River.

Louisville, Kentucky was founded at the only major natural navigational barrier on the river, the Falls of the Ohio. These were a series of rapids where the river flowed over hard, fossil-rich beds of limestone. The first locks on the river were built at Louisville to circumnavigate the falls. Today, this is the site of McAlpine Locks and Dam.

Because the Ohio River flowed westwardly, it became the convenient means of westward movement by pioneers from western Pennsylvania to St. Louis, Missouri, where some continued on up the Missouri River, some up the [Mississippi River, and some further west over land routes. In these early days, in the early 1800s, pirates set up shop at Cave-in-Rock in southern Illinois, waylaid settlers on their way down the river, killed them, stole their goods, and scuttled their boats.

Because of its significant role as the southern border of Ohio, Indiana, and Illinois, the Ohio River is historically famous as the border dividing free states and slave states. As depicted in several novels by Harriet Beecher Stowe and Toni Morrison, the Ohio River was the barrier which, by crossing by boat or 'on ice floes', slaves were freed. Today, the Ohio River generally separates Midwestern and Great Lakes states from Southern border states.

Interestingly, by an accident of history, the charter for Virginia went not to the middle of the Ohio River, but to its far shore so the entire river was included. Wherever the river serves as a boundary between states -- Illinois, Indiana, and Ohio on the north, and Kentucky and West Virginia on the south, the river essentially belongs to the two states on the south that were divided from Virginia. Kentucky brought suit against Indiana in the early 1980s because of the building of the Marble Hill nuclear power plant in Indiana, which would have discharged its waste water into the river. The U.S. Supreme Court ruled that Kentucky's jurisdiction (and, implicitly, that of West Virginia) extended only to the low water mark of 1793, important because the river has been extensively dammed for navigation, so that the present river bank is north of the old low water mark.

In the early 1980s, the Falls of the Ohio National Wildlife Conservation Area was established at Louisville, Kentucky.

Cities along the Ohio

Besides Pittsburgh and Cairo, other cities along the Ohio include: