Ohio

Course and watershed

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 Indians and early European 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) were considered a strategic military location by colonial French and British, and later independent American military authorities.

The Ohio River is formed by the confluence of the Allegheny and Monongahela rivers at what is now Point State Park in Pittsburgh, Pennsylvania.

History

The river had great significance in the history of the Native Americans, as numerous prehistoric and historic civilizations formed along its valley. For thousands of years, Native Americans used the river as a major transportation and trading route.

In the five centuries before European colonization, the Mississippian culture built numerous regional chiefdoms and major earthwork mounds in the Ohio Valley like the Angel Mounds near Evansville, Indiana as well as in the Mississippi Valley and the Southeast. The historic Osage, Omaha, Ponca, and Kaw peoples lived in the Ohio Valley. Under pressure over the fur trade from the Haudenosaunee 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.

Ecology

The Ohio River is home to diverse ecosystems and a host of different species. Between 1817 and 1983, there were 154 species of fish found in the river. Only 14 of those species were introduced by humans. Since 1900, there has been an exponential decrease in species of fish that were previously plentiful, like shovelnose sturgeon, paddlefish, muskellunge, and blue sucker. The river also contains over 50 different species of mussels and supports a wide array of birds. Invasive species that have been introduced through anthropogenic means are also present in the river and are in part responsible for this species depletion. For example, zebra mussels and Asian carp both compete with local species for food, causing the decline in some species.

Geology

From a geological standpoint, the Ohio River is young. Before the river was created, large parts of North America were covered by water forming a saltwater lake about 200 miles across and 400 miles in length. The bedrock of the Ohio Valley was mostly set during this time. The river formed on a piecemeal basis beginning between 2.5 and 3 million years ago.