The Allegheny River is a principal tributary of the Ohio River and is located in the Eastern United States. It joins with the Monongahela River to form the Ohio River at "The Point" of Point State Park in Downtown Pittsburgh, Pennsylvania.
The river is approximately long, running through the U.S. states of New York and Pennsylvania. It drains a rural dissected plateau of in the northern Allegheny Plateau, providing the northeastern most drainage in the watershed of the Mississippi River. Its tributaries reach to within of Lake Erie in southwestern New York. The valley of the river has been one of the most productive areas of energy extraction in U.S. history, with extensive deposits of coal, petroleum, and natural gas.
The word Allegheny comes from the Lenape (Delaware) Indians. Although it is usually translated as "fine river", the meaning is not definitively known. There is a Lenape legend of a tribe called "Allegewi" who used to live along the river. Other Indians, such as the Iroquois, considered the Allegheny and Ohio rivers as the same, as is suggested by a New York State road sign on Interstate 86 that refers to the Allegheny river secondarily as O Hi Yo. Areas around the river, in the State of New York, are often named with an alternate spelling Allegany in reference to the river, such as the Village of Allegany, New York.
The Allegheny rises in north central Pennsylvania, in central Potter County, approximately 10 miles (16 km) south of the New York border. It flows west past Coudersport then turns north into western New York State, looping westward across southern Cattaraugus County for approximately 30 miles (48 km), past Portville, Olean, St. Bonaventure University and Salamanca and forming the northern boundary of Allegany State Park before re-entering northwestern Pennsylvania approximately 20 miles (32 km) southeast of Jamestown, New York.
It flows in a broad zigzag course generally southward across western Pennsylvania, first flowing southwest past Warren, Oil City, and Franklin, forming much of the northwestern boundary of Allegheny National Forest. South of Franklin it turns southeast across Clarion County in a meandering course, then turns again southwest across Armstrong County, flowing past Kittanning, Ford City, Clinton and Freeport. It enters Allegheny County, the Pittsburgh suburbs, and the City of Pittsburgh from the northeast passing Sligo, Karns, and Natrona in Harrison Township, then Braeburn, Lower Burrell, Brackenridge, Tarentum, Creighton, Arnold, New Kensington, Springdale, Harmarville, Blawnox, Fox Chapel, Sharpsburg, Etna, Millvale, Lawrenceville, Highland Park, The North Side, Downtown Pittsburgh, Point State Park and joins with the Monongahela River at "The Point" in Downtown Pittsburgh, Pennsylvania to form the Ohio River. Water from the Allegheny River eventually flows into the Gulf of Mexico via the Ohio River and the Mississippi River.
In its upper reaches the Allegheny is joined from the south by Potato Creek in McKean County, Pennsylvania and from the north by Olean Creek at Olean, New York. The Great Valley Creek and Little Valley Creek join the river from the north in Salamanca, New York before becoming the Allegheny Reservoir. After re-entering Pennsylvania, it is joined from the east by Kinzua Creek 10 miles (16 km) upstream of Warren; from the north by Conewango Creek at Warren; from the west by Brokenstraw Creek; from the north by Oil Creek at Oil City; from the west by French Creek at Franklin; from the east by the Clarion River in Parker, Pennsylvania, one of its principal tributaries, in eastern Clarion County; from the east by Crooked Creek southeast of Kittanning; and from the east by the Kiskiminetas River, another principal tributary, at Freeport. Buffalo Creek enters at Freeport, Bull Creek enters at Tarentum. There are many other creeks, runs and streams that enter or join with the Allegheny River.
In the 16th century, control of the river valley passed back-and-forth between Algonquian-speaking Shawnee and the Iroquois. By the time of the arrival of the French in the early 18th century, the Shawnee were once again in control and formed an alliance with the French against the incursion of British settlement across the Allegheny Mountains. The conflict over the expansion of British settlement into the Allegheny Valley and the surrounding Ohio Country was a primary cause of the French and Indian War in the 1750s. During the war, the village of Kittaning, the principal Shawnee settlement on the river, was completely destroyed by British reprisal raids from central Pennsylvania.
Nevertheless, the British, after gaining control of the area in the 1763 Treaty of Paris, kept the area closed to white settlement, in part to repair and maintain relations with the Native Americans. The pressure to open the river valley and the surrounding area to settlement is considered by historians to be one of the root causes of the American Revolutionary War in the following decade.
During the 19th century, the river became a principal means of navigation in the upper Ohio valley, especially for the transport of coal. Although the building of the railroads lessened the importance of the river somewhat, the lower river (navigable as far as East Brady, Pennsylvania through locks) has continued to serve as route of commercial transportation until the present day. In 1859, the first U.S. petroleum was drilled north of the river at Titusville.
In 1965, the completion of the federally-sponsored Kinzua Dam for flood-control in northwestern Pennsylvania east of Warren created the long Allegheny Reservoir, part of which is included in the Allegheny National Recreation Area. The dam flooded parts of lands deeded "forever" to the Seneca tribe and to Cornplanter and his descendants. (The event is described in the Johnny Cash tune "As Long as the Grass Shall Grow.")