The Allegheny River ( AL-ig-AY-nee; Seneca: Ohi:yo'; Unami: Alikehane) is a 325-mile-long (523 km) river that is located in western Pennsylvania and western New York in the United States. The chief tributary of the Ohio River, the Allegheny runs from its headwaters just below the center of Pennsylvania’s northern border, heads northwest into Western New York, then zigzags southwesterly back across the border to flow through Western Pennsylvania and finally join the Monongahela River at Forks of the Ohio near Downtown Pittsburgh, Pennsylvania.
The Allegheny River is, by volume, the main headstream of both the Ohio and Mississippi Rivers. Historically, the Allegheny was considered to be the upper Ohio River by both Native Americans and European settlers.
This shallow river has been made navigable upstream from Pittsburgh to East Brady by a series of locks and dams that were constructed during the early 20th century. A 24-mile-long portion of the upper river in Warren and McKean counties of Pennsylvania and Cattaraugus County in New York forms the Allegheny Reservoir, which was created by the erection of the Kinzua Dam in 1965 for flood control.
The etymology behind the word "Allegheny" is of unclear pre-Columbian origin and may be derived from one of a number of Delaware/Unami phrases that are homophones of the English name, with varying translations.

Quelle: Wikipedia