Tioga River (Chemung River)
The Tioga River (// TIE-o-guh) is a tributary of the Chemung River, approximately 58 miles (93 km) long, in northern Pennsylvania and western New York in the United States. It drains a region of ridges in the northern Allegheny Plateau in the watershed of the Susquehanna River.
It rises in the mountains of western Bradford County and flows initially southwest into Tioga County, passing through Tioga State Forest. In southern Tioga County it turns north, cutting gaps in four separate ridges while flowing past Blossburg and Mansfield, then through Tioga Reservoir. North of Tioga it receives Crooked Creek from the west, then crosses into Steuben County, New York, near Lawrenceville, Pennsylvania. It receives the Cowanesque River from the west approximately 1 mi (2 km) north of the state line, then receives the Canisteo River from the west in southwestern Steuben County, approximately 10 mi (15 km) southwest of Corning. It joins the Cohocton River at Painted Post, just west of Corning, to form the Chemung, a tributary of the Susquehanna.
In the 19th century the Tioga Valley supported a large shipbuilding industry. Logs were floated down the Tioga and the Chemung to the Susquehanna River and on to the Chesapeake Bay and the shipyards of Baltimore.
Tioga Reservoir 
The Tioga River has one major impoundment, the Tioga Reservoir, formed by a dam just after the borough of Tioga, Pennsylvania and just before it receives Crooked Creek. The lake has a surface area of 498 acres (2.02 km2) and is administered by the United States Army Corps of Engineers, which built the Tioga Dam from 1973 to 1979. Built together with the adjoining Hammond Dam and Hammond Lake (on Crooked Creek), the total project cost $200 million.
The dam projects were initially authorized by the United States Congress in the Flood Control Act of 3 July, 1958 (Public Law 85-500). Construction was begun in the aftermath of the devastating floods caused by Hurricane Agnes in June 1972. A channel connects the two lakes so that Hammond Lake (which has greater storage capacity) may be used to store excess (flood) water from Tioga Lake.
However, in addition to flood control on the Chemung and Susquehanna rivers, the dams are also meant to help decrease the acidity of water in the Tioga River downstream of the dams by dilution with the more neutral waters of Crooked Creek. The Tioga River's acidity is caused by acid mine drainage.
See also 
- U.S. Geological Survey. National Hydrography Dataset high-resolution flowline data. The National Map, accessed August 8, 2011
- U.S. Geological Survey: PA stream gaging stations
- Rootsweb: Tioga River history
- U.S. Army Corps of Engineers page on Tioga-Hammond Lakes
- History of the Hammond-Tioga Dam Project
- Chesapeake Bay Program - The Tioga River Watershed
- Chesapeake Bay Program - Tioga River - Canisteo River To Chemung River Watershed