The Allegheny River is a 325-mile (523 km) long headwater stream of the Ohio River in western Pennsylvania and New York, United States. The Allegheny River runs from its headwaters just below the middle of Pennsylvania’s northern border northwesterly into New York then in a zigzag southwesterly across the border and through Western Pennsylvania to join the Monongahela River at the Forks of the Ohio on the “Point” of Point State Park in Downtown Pittsburgh, Pennsylvania. The Allegheny River is, by volume, the main headstream of both the Ohio and Mississippi Rivers. Historically, the Allegheny was considered the upper Ohio River by both Native Americans and European settlers.
A succession of locks and dams built in the early twentieth century made the shallow river passable upstream from Pittsburgh to East Brady. The Allegheny Reservoir, commonly known as Lake Kinzua, is a 24-mile-long section of the upper river between Warren and McKean counties in Pennsylvania and Cattaraugus County in New York, formed by the construction of the Kinzua Dam in 1965 for flood control.
The name of the river comes from one of a number of Delaware/Unami phrases that are homophones of the English name, with varying translations.