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. (March 2017)
The widest point on the Ohio River is just north of downtown Louisville
, where it is one mile (1.6 km) wide
|States||Pennsylvania, Ohio, West Virginia, Kentucky, Indiana, Illinois|
| - left||Little Kanawha River, Kanawha River, Guyandotte River, Big Sandy River, Little Sandy River, Licking River, Kentucky River, Salt River, Green River, Cumberland River, Tennessee River|
| - right||Beaver River, Little Muskingum River, Muskingum River, Little Hocking River, Hocking River, Shade River, Scioto River, Little Miami River, Great Miami River, Wabash River|
|Cities||Pittsburgh, PA, East Liverpool, OH, Wheeling, WV, Parkersburg, WV, Huntington, WV, Ashland, KY, Cincinnati, OH, Louisville, KY, Owensboro, KY, Evansville, IN, Henderson, KY, Paducah, KY, Cairo, IL|
| - location||Allegany Township, Potter County, Pennsylvania|
| - elevation||2,240 ft (683 m)|
| - coordinates||41°52′22″N 77°52′30″W / 41°52′22″N 77°52′30″W / 41.87278; -77.87500|
|Secondary source||Monongahela River|
| - location||Fairmont, West Virginia|
| - elevation||880 ft (268 m)|
| - coordinates||39°27′53″N 80°09′13″W / 39°27′53″N 80°09′13″W / 39.46472; -80.15361|
| - location||Pittsburgh, Pennsylvania|
| - elevation||730 ft (223 m)|
| - coordinates||40°26′32″N 80°00′52″W / 40°26′32″N 80°00′52″W / 40.44222; -80.01444|
| - location||at Cairo, Illinois / Ballard County, Kentucky|
| - elevation||290 ft (88 m)|
| - coordinates||36°59′12″N 89°07′50″W / 36°59′12″N 89°07′50″W / 36.98667; -89.13056|
|Length||981 mi (1,579 km)|
|Basin||189,422 sq mi (490,601 km2)|
|Discharge||for Cairo, Illinois|
| - average||281,000 cu ft/s (7,957 m3/s) (1951–80)|
| - max||1,850,000 cu ft/s (52,386 m3/s)|
Ohio River basin
The Ohio River, which streams westward from Pittsburgh, Pennsylvania, to Cairo, Illinois, is the largest tributary, by volume, of the Mississippi River in the United States. At the confluence, the Ohio is considerably bigger than the Mississippi (Ohio at Cairo: 281,500 cu ft/s (7,960 m3/s); Mississippi at Thebes: 208,200 cu ft/s (5,897 m3/s)) and, thus, is hydrologically the main stream of the whole river system.
The 981-mile (1,579 km) river flows through or along the border of six states, and its drainage basin includes parts of 15 states. Through its largest tributary, the Tennessee River, the basin includes many of the states of the southeastern U.S. It is the source of drinking water for three million people.
It is named in Iroquoian or Seneca: Ohi:yó, lit. "Good River" or Shawnee: Pelewathiipi and Spelewathiipi. The river had great significance in the history of the Native Americans, as numerous civilizations formed along its valley. For thousands of years, Native Americans used the river as a major transportation and trading route. Its waters connected communities. In the five centuries before European conquest, the Mississippian culture built numerous regional chiefdoms and major earthwork mounds in the Ohio Valley, such as Angel Mounds near Evansville, Indiana, as well as in the Mississippi Valley and the Southeast. The Osage, Omaha, Ponca and Kaw lived in the Ohio Valley, but under pressure from the Iroquois to the northeast, migrated west of the Mississippi River to Missouri, Arkansas and Oklahoma in the 17th century.
In 1669, René-Robert Cavelier, Sieur de La Salle led a French expedition to the Ohio River, becoming the first Europeans to see it. After European-American settlement, the river served as a border between present-day Kentucky and Indian Territories. It was a primary transportation route for pioneers during the westward expansion of the early U.S. In his Notes on the State of Virginia published in 1781–82, Thomas Jefferson stated: "The Ohio is the most beautiful river on earth. Its current gentle, waters clear, and bosom smooth and unbroken by rocks and rapids, a single instance only excepted."
During the 19th century, the river was the southern boundary of the Northwest Territory. It is sometimes considered as the western extension of the Mason–Dixon Line that divided Pennsylvania from Maryland, and thus part of the border between free and slave territory, and between the Northern and Southern United States or Upper South. Where the river was narrow, it was the way to freedom for thousands of slaves escaping to the North, many helped by free blacks and whites of the Underground Railroad resistance movement.
The Ohio River is a climatic transition area, as its water runs along the periphery of the humid subtropical and humid continental climate areas. It is inhabited by fauna and flora of both climates. In winter, it regularly freezes over at Pittsburgh but rarely farther south toward Cincinnati and Louisville. At Paducah, Kentucky, in the south, near the Ohio's confluence with the Mississippi, it is ice-free year-round.