The Allegheny River (// AL-ə-GAE-nee) 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 to be the upper Ohio River by both Native Americans and European settlers.
|State||Pennsylvania, New York|
|• location||Allegany Township, Potter County, Pennsylvania, near Coudersport, Pennsylvania at the corner of Ben Green and Cobb Hill Rd|
|• elevation||2,450 feet (750 m)|
|Ohio River at Pittsburgh, Pennsylvania|
|712 feet (217 m)|
|Length||325 miles (523 km)|
|Basin size||11,580 square miles (30,000 km2)|
|• average||19,750 cu ft/s (559 m3/s) at the village of Natrona, PA (river mile 24.3)|
|Progression||Allegheny River → Ohio River → Mississippi River → Gulf of Mexico|
|• left||Tionesta Creek, Clarion River, Redbank Creek, Mahoning Creek, Crooked Creek, Kiskiminetas River, Buffalo Creek, Chartiers Run|
|• right||Conewango Creek, Brokenstraw Creek, Oil Creek, French Creek, Bull Creek, Deer Creek, Squaw Run, Pine Creek, Girtys Run, Pucketa Creek|
|Designated||April 20, 1992|
The shallow river has been made navigable upstream from Pittsburgh to East Brady by a series of locks and dams constructed in 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 is the Allegheny Reservoir also known as Lake Kinzua, created by the erection of the Kinzua Dam in 1965 for flood control.