In 1830, the Louisville and Portland Canal (now the McAlpine Locks and Dam) bypassed the rapids, allowing even larger commercial and modern navigation from the Forks of the Ohio at Pittsburgh to the Port of New Orleans at the mouth of the Mississippi on the Gulf of Mexico.

Its current gentle, waters clear, and bosom smooth and unbroken by rocks and rapids, a single instance only excepted.

The river 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 crossed by thousands of slaves escaping to the North for freedom; many were helped by free blacks and whites of the Underground Railroad resistance movement.

[18] The river had great significance in the history of the Native Americans, as numerous prehistoric and historic civilizations formed along its valley.

Under pressure over the fur trade from the Iroquois nations to the northeast, they migrated west of the Mississippi River in the 17th century to the territory now defined as Missouri, Arkansas, and Oklahoma.

[42] The bones were collected and shipped to Paris, where they were identified as mastodon remains; they are on display at the French National Natural History Museum.

[32] He led an expedition of 442 men, including Native Americans, from Montreal to war against the Chickasaw who occupied territory on the lower part of the Mississippi River in the area claimed as La Louisiane.

The rank and file consisted of three sergeants, six corporals, six lance corporals, twenty-four soldiers, forty-five habitants, one hundred and eighty-six Iroquois from the Sault, forty-one from the Lake of Two Mountains, thirty-two Algonquin and Nipissing, fifty Abenaqui from St. Francois and Bécancour, Quebec; Father La Bretonnier, Jesuit; Queret, missionary.

[46] The elder Howard had a promised reward of 10,000 acres (4,000 ha) of land for a successful expedition from the Virginia Royal Governor's Council to reinforce British claims in the west.

The Virginia pioneers traced the northern boundary of Kentucky for five hundred miles (800 km), reaching the Mississippi River on June 7.

[47][48][49][50][51] They descended just below the mouth of the Arkansas River, where they were ambushed by a large company of Native Americans, Blacks and Frenchmen on July 2, 1742; one or two of Howard's men were killed.

The movement across the Allegheny Mountains of Anglo-American settlers and the claims of the area near modern-day Pittsburgh led to conflict with the French, who had forts in the Ohio River Valley.

The 1768 Treaty of Fort Stanwix with several tribes opened Kentucky to colonial settlement and established the Ohio River as a southern boundary for American Indian territory.

Lord Dunmore's War south of the Ohio river also contributed to cession of land north to Quebec to prevent colonial expansion onto Native American territory.

[54] However, the 1783 Treaty of Paris gave the entire Ohio Valley to the United States, and numerous white settlers entered the region.

It was renovated again in 1872, and remains in use as the oldest vehicular suspension bridge in the U.S. Louisville was founded in 1778 as a military encampment on Corn Island (now submerged) by General George Rogers Clark at the only major natural navigational barrier on the river, the Falls of the Ohio.

Fears that Louisville's transshipment industry would collapse proved ill-founded: but the increasing size of steamships and barges on the river meant that the outdated locks could serve only the smallest vessels until well after the Civil War when improvements were made.

During the nineteenth century, emigrants from Virginia, North Carolina and Kentucky traveled by the river and settled along its northern bank.

Trading boats and ships traveled south on the Mississippi to New Orleans, and sometimes beyond to the Gulf of Mexico and other ports in the Americas and Europe.

[60] More escaping slaves, estimated in the thousands, made their perilous journey north to freedom across the Ohio River than anywhere else across the north-south frontier.

She also composed the libretto for the opera Margaret Garner (2005), based on the life and trial of an enslaved woman who escaped with her family across the river.

Similarly, in the 1990s, Kentucky challenged Illinois's right to collect taxes on a riverboat casino docked in Metropolis, citing its own control of the entire river.

The Commission found that 92% of toxic discharges were nitrates, including farm runoff and waste water from industrial processes such as steel production.

[64] The Ohio was listed among America's Most Endangered Rivers of 2023 on the heels of contamination from a high-profile train derailment, and following years as one of the most polluted watersheds in the United States.

Major cities located along the northern and southern banks of the river include Pittsburgh, Pennsylvania; Louisville, Kentucky; Evansville, Indiana; and Cincinnati, Ohio.

[21] The combined Allegheny-Ohio river is 1,310 miles (2,110 km) long and carries the largest volume of water of any tributary of the Mississippi.

The dams raise the water level and have turned the river largely into a series of reservoirs, eliminating shallow stretches and allowing for commercial navigation.

Prior to that event, the north-flowing Steubenville River (no longer in existence) ended between New Martinsville and Paden City, West Virginia.

Annual events taking place on or over the river include Thunder Over Louisville, the Madison Regatta, and the Great Steamboat Race.