The
Ohio River is the largest
tributary, by volume, of the
Mississippi River. It is approximately 981 miles (1,579 km) long and is located in the eastern
United States.
The river had great significance in the history of the
Native Americans, as numerous civilizations formed along its valley. In the last five centuries prior to European contact, the
Mississippian culture built numerous regional
chiefdoms and major
earthwork mounds in the Ohio Valley, such as
Angel Mounds near
Evansville, Indiana. For thousands of years, Native Americans, like the European explorers and settlers who followed them, used the river as a major transportation and trading route. About 1200
CE, the area of Kentucky was the site of longterm wars between the
Iroquois, invading from present-day New York, and the
Osage and other Ohio River tribes. Over centuries, the Osage,
Omaha,
Ponca and
Kaw migrated west of the
Mississippi River, settling by the mid-17th century in their
historic grounds in
Missouri,
Arkansas, and
Oklahoma, and nearby states.
After European-American settlement, the river served at times as a border between present-day
Kentucky and
Indian Territories. It was a primary transportation route during the westward expansion of the early U.S. The Ohio flows through or along the border of six
states, and its
drainage basin encompasses 14 states. Through its largest tributary, the
Tennessee River, the basin includes many of the states of the
southeastern U.S.During the nineteenth century, the river was the southern boundary of the
Northwest Territory, thus serving as the border between free and
slave territory. It is sometimes referred to as the "
Mason-Dixon line". It is commonly acknowledged as the western natural extension of the original Mason-Dixon line that divided
Pennsylvania and
Delaware from
Maryland and
West Virginia (then a part of
Virginia.) It was thus the unofficial and, at times disputed, border between the
Northern United States and the
American South or
Upper South.
The Ohio River is a
climatic transition area, as its water runs along the periphery of the
humid subtropical climate and
humid continental climate. It is inhabited by fauna and flora of both climates. 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."
Geography and hydrography
The river is formed by the confluence of the
Allegheny and
Monongahela rivers.
Point State Park in
Pittsburgh, Pennsylvania marks the confluence. From Pittsburgh, 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 (near
East Liverpool, Ohio,
Chester, West Virginia, and
Midland, Pennsylvania). 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. It flows along the borders of West Virginia,
Ohio,
Kentucky,
Indiana, and
Illinois, until it joins the
Mississippi near the city of
Cairo, Illinois.
Major tributaries of the river, indicated by the location of the mouths, include:
Drainage basin
The Ohio's drainage basin covers 189,422 square miles (490,603 km²), including the easternmost regions of the
Mississippi Basin. States drained by the Ohio include:
- Illinois (the southeast quarter of the state),
- Indiana (all but the northern area of the state),
- Ohio (the southern half of the state),
- Pennsylvania (a corridor from the southwestern corner to north central border),
- Georgia (the northwest corner of the state),
Geology
From a geologic standpoint, the Ohio River is young. The river formed on a piecemeal basis beginning between 2.5 and 3 million years ago. The earliest
Ice Ages occurred at this time and dammed portions of north-flowing rivers. The
Teays River was the largest of these rivers. The modern Ohio River flows within segments of the ancient Teays. The ancient rivers were rearranged or consumed by
glaciers and lakes.
Upper Ohio River
The upper Ohio River formed when one of the glacial lakes overflowed into a south-flowing tributary of the
Teays River. Prior to that event, the north-flowing Steubenville River (no longer in existence) ended between
New Martinsville and
Paden City, West Virginia. Likewise, the south-flowing Marietta River (no longer in existence) ended between the present-day cities. The overflowing lake carved through the separating hill and connected the rivers.
The resulting floodwaters enlarged the small
Marietta valley to a size more typical of a large river. The new large river subsequently drained glacial lakes and melting glaciers at the end of several
Ice Ages. The valley grew with each major
Ice Age.
Many small rivers were altered or abandoned after the upper Ohio River formed. Valleys of some abandoned rivers can still be seen on satellite and aerial images of the hills of
Ohio and West Virginia between
Marietta, Ohio, and
Huntington, West Virginia. As testimony to the major changes that occurred, such valleys are found on hilltops.
Middle Ohio River
The middle Ohio River formed in a manner similar to formation of the upper Ohio River. A north-flowing river was temporarily dammed southwest of present-day
Louisville, Kentucky, creating a large lake until the dam burst. A new route was carved to the
Mississippi River. Eventually the upper and middle sections combined to form what is essentially the modern Ohio River.
History
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 tributary of the Mississippi River. The river is 981 miles (1,579 km) long and carries the largest volume of water of any tributary of the Mississippi. The Indians and early explorers and settlers of the region often considered the Allegheny to be part of the Ohio. The
forks (the confluence of the Allegheny and Monongahela rivers at what is now Pittsburgh) was considered a strategic military location.
In 1669
René-Robert Cavelier, Sieur de La Salle, led an
expedition of French traders who became the first Europeans to see the river. He traveled from
Canada and entered the headwaters of the Ohio, traveling as far as the Falls of Ohio before turning back. He returned to explore the river again in other expeditions. An
Italian cartographer traveling with him created the first map of the Ohio River. France claimed ownership of the river until its territory in North America was ceded to Great Britain in 1763, following the
Seven Years War (aka the
French and Indian War.)
On
May 19,
1749, King
George II of Great Britain granted the
Ohio Company a charter of land around the forks. Exploration of the territory and trade with the Indians in the region near the Forks by
British colonials from Pennsylvania and Virginia—both of which claimed the territory—led to conflict with
French forces that also claimed the region and had built forts along the Allegheny River. This directly led to the French and Indian War in North America. The French and Indian War was part of a more global conflict, the
Seven Years' War between England and France. After several initial defeats, the British eventually gained sovereignty over the Ohio Valley.
The 1768
Treaty of Fort Stanwix opened Kentucky to colonial settlement and established the Ohio River as a southern boundary for American Indian territory. In 1774, the
Quebec Act restored the land east of the Mississippi River and north of the Ohio River to Quebec, appeasing the French-speaking British subjects, but angering the
Thirteen Colonies. They listed it as one of the
Intolerable Acts which precipitated the
American Revolution.
Louisville, Kentucky was founded at the only major natural navigational barrier on the river, the
Falls of the Ohio. The Falls were a series of rapids where the river dropped in a stretch of about . In this area, the river flowed over hard, fossil-rich beds of
limestone. The first
locks on the river were built in 1825 at Louisville to circumnavigate the falls. Today it is the site of
McAlpine Locks and Dam.
Because the Ohio River flowed westwardly, it became a convenient means of westward movement by pioneers traveling from western Pennsylvania. After reaching the mouth of the Ohio, settlers would travel north on the Mississippi River to
St. Louis, Missouri. There, some continued on up the
Missouri River, some up the Mississippi, and some further west over land routes. In the early 19th century,
pirates such as
Samuel Mason, settled at
Cave-In-Rock, Illinois, waylaid travelers on their way down the river. They killed travelers, stealing their goods and scuttling their boats. The folktales about
Mike Fink recall the
keelboats used for commerce in the early days of European settlement. The Ohio River boatmen were the inspiration for performer
Dan Emmett, who in 1843 wrote the song "
The Boatman's Dance".
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. This provided a much-needed export route for goods from the west, since the trek east over the
Appalachian Mountains was long and arduous. The need for access to the port of New Orleans by settlers in the Ohio Valley led to the
Louisiana Purchase in 1803.
Because the river is the southern border of Ohio, Indiana and Illinois, it was part of the border between free tates and slave states in the years before the
American Civil War. The expression "sold down the river" originated as a lament of Upper South
slaves, especially from Kentucky, who were separated from their families and sold in Louisville and other Kentucky locations to be shipped via the Ohio River and Mississippi down to New Orleans. There they were sold to owners of cotton and sugar field plantations in the Deep South, which were notoriously hard on laborers. Before and during the Civil War, the Ohio River was called the "River Jordan" by slaves' crossing it to escape to freedom in the North via the
Underground Railroad. Such escapes were depicted in contemporary anti-slavery novels, such as
Harriet Beecher Stowe's
Uncle Tom's Cabin. The times have also been portrayed by late 20th century novelists such as
Toni Morrison. More escaping slaves made their perilous journey north to freedom across the Ohio River than anywhere else across the north-south frontier.
Today, the Ohio River is considered to separate
Midwestern Great Lakes states from
Southern states which were historically
border states in the Civil War.
Mouth of the Ohio, as it feeds into the Mississippi
The charter for
Virginia went to the far shore of the Ohio River, so that the entire river was included in the lands "owned" by Virginia. Where the river serves as a boundary between states today, the entire river belongs to the states on the east and south, i.e., West Virginia and Kentucky, that were divided from Virginia. Thus
Wheeling Island, the largest inhabited island in the Ohio River, belongs to West Virginia, even though it is closer to the Ohio shore than to the West Virginia shore. 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 held 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.) Similarly, in the 1990s, Kentucky challenged Illinois' right to collect taxes on a riverboat casino docked in
Metropolis, citing its own control of the entire river. A private casino riverboat that docked in
Evansville, Indiana on the Ohio River opened about the same time. Although such boats cruised on the Ohio River in an oval pattern up and down, the state of Kentucky soon protested. Other states had to limit their cruises to going forwards then reversing and going backwards on the Indiana shore only.
In the early 1980s, the
Falls of the Ohio National Wildlife Conservation Area was established at
Clarksville, Indiana.
River depth
The Ohio River is a naturally shallow river that was artificially deepened by series of
dams. 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. Near its origin at the confluence of the
Allegheny and
Monongahela Rivers, the Ohio remains fairly shallow, never rising above around deep all the way past Cincinnati. From its origin to Cincinnati, the average depth is approximately . However, once past Cincinnati, the river deepens substantially. Due to the damming, along with
glacier formations and migrations in the latter part of the
second Ice Age, the river's depth increases nearly fivefold over about , coming to a maximum depth of just west of
Louisville, Kentucky. The around Louisville represent the deepest area of the river with an average depth of approximately , allowing for much larger vessels to traverse the river. From Louisville, the river loses its depth very gradually until its confluence with the Mississippi at
Cairo, Illinois, where it has an approximate depth of , because it is more free flowing. The natural depth of the river varies from about 3 feet to 40 feet.
Water levels for the Ohio River are predicted daily by the
National Oceanic and Atmospheric Administration's . The water depth predictions are relative to each local flood plain based upon predicted rainfall in the Ohio River basin in five reports as follows:
Cities and towns along the river
Cities along the Ohio include:
Recreation
The
world record for the largest
blue catfish taken in the line class was set on the Ohio River in 1999. The river also holds records for the following species for the state of Kentucky:
The Ohio River from
Cairo, Illinois to
Smithland, Kentucky comprises a significant portion of the
Great Loop, the circumnavigation of Eastern North America by water for recreational purposes.
