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. The 981-mile river flows through or along the border of six 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 and 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, 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 served as a border between present-day Kentucky and Indian Territories. It was a 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 and 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 boundary of the Northwest Territory. 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 transition area, as its water runs along the periphery of the humid subtropical. It is inhabited by fauna and flora of both climates, in winter, it regularly freezes over at Pittsburgh but rarely further south toward Cincinnati and Louisville. At Paducah, Kentucky, in the south, near the Ohios confluence with the Mississippi, Paducah was founded there because it is the northernmost ice-free reach of the Ohio. The Ohio River is formed by the confluence of the Allegheny and Monongahela rivers at Point State Park in Pittsburgh, from there, it flows northwest through Allegheny and Beaver counties, before making an abrupt turn to the south-southwest at the West Virginia–Ohio–Pennsylvania triple-state line. From there, it forms the border between West Virginia and Ohio, upstream of Wheeling, West Virginia, the river then follows a roughly southwest and then west-northwest course until Cincinnati, before bending to a west-southwest course for most of its length. The course forms the borders of West Virginia and Kentucky. The Ohio drains parts of 15 states in four regions, northeast New York, a small area of the southern border along the headwaters of the Allegheny. Pennsylvania, a corridor from the corner to north central border
The widest point on the Ohio River is just north of downtown Louisville, where it is one mile (1.6 km) wide
Natural-color satellite image of the Wabash-Ohio confluence.
Glacial Lake Ohio
Steamboat "Morning Star", a Louisville and Evansville mail packet, in 1858.