The Upper Ohio River Basin

The Ohio River and its tributaries represent one of the most diverse freshwater ecosystems on earth. This is particularly demonstrated by a richness of fish and mollusk species. The Ohio and Allegheny rivers have been identified as important ecosystems for conservation from the basin source here in Pennsylvania as well as downstream across the Midwest. However, habitat and ecosystem qualities are not equal along the 981-mile course of the Ohio River, the 321-mile length of the Allegheny River, nor their tributaries.

Although historically more widely distributed, today the most significant biodiversity of the Ohio River Basin in Pennsylvania is found within the Allegheny River, especially the middle free-flowing section from Kinzua Dam downstream to East Brady, where the navigational lock-and-dam system begins. This reach of the basin also includes the river’s most diverse tributary, French Creek, and other large subbasins, such as the Clarion River. Other important sections of the Ohio Basin include the headwaters of  the Allegheny River Basin in north western Pennsylvania and New York, certain tributaries of the lower Allegheny River, e.g. Mahoning Creek, and the middle reach of the Shenango River, which is within the Beaver River system.

Large rivers represent the most imperiled types of ecosystems in North America, and the condition of the Ohio River and its major tributaries are no exception. The lowest miles of the Allegheny River and all of the Ohio River exist today as “working rivers”, flowing slowly as a network of dammed navigational pools. These rivers are also flowing through largely urbanized and industrialized landscapes, which include sub-basins heavily influenced by a legacy of coal mining, and main river channels managed largely for commercial interests. However, even here, it is important to protect and improve biodiversity health and values. Conservation planning should focus on issues of water quality, river depth, river currents and free-flow conditions, type of river bed (gravel, sand, etc.) and population viability of aquatic species. As in the upper less constrained portions of the basin, the health of fishes and freshwater mussels will ultimately tell the story of the condition of our river ecosystems.

Key Features

  • Free-flowing river segments with good water quality and diverse habitats
  • Tributaries that retain species of aquatic life that have declined elsewhere
  • Improving water quality in lower reaches and the ongoing return of aquatic species and health of some aquatic populations (fish, mussels)

Conservation Targets

  • 600 miles of high quality major river and tributary ecosystems
  • Additional river and tributary segments as restoration reaches to regain downstream and upstream linkages, especially the lower 72 miles of the Allegheny River and the first 50+ miles of the Ohio River, where there are opportunities to recreate the best possible river habitats
  • More than 500 occurrences of globally rare plants, invertebrates, vertebrates and aquatic communities including the northern riffleshell mussel and the bluebreast darter
  • Two dozen Biological Diversity Areas: highly significant habitats, including island groups: 1,400 acres
  • 200 important forest patches, especially in the upper basin, some of which adjoin the stream riparian zones.

Riparian Zone (n). The land adjacent to a stream or river, beginning at the stream bank and extending away from the bank into the floodplain where the land is level. Riparian zone widths vary.

Upper Allegheny River

The Upper Allegheny Region of northwestern Pennsylvania and southwestern New York begins at the headwaters of the Allegheny River west of Coudersport, Pennsylvania and extends north to Lake Chatauqua in New York and south to the Clarion River in Pennsylvania.

Lower Allegheny River & Ohio River Mainstem

The Ohio River is one of the most biodiversity-rich river systems in the world. This distinction, however, is not consistent along the river’s entire length or across all of its tributary basins.

Allegheny & Ohio River Tributaries

Ultimately, a river’s quality is only as good as the water it receives from its tributaries. Any particular reach of the Ohio or Allegheny rivers, for example, is greatly influenced by thousands of miles of tributary watersheds that congregate to influence larger streams.


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