FIGURE 2-1 Ohio River basin showing locks and dams along the Ohio River; boxed area includes the Allegheny and Monongahela River basins and the headwaters of the Ohio River in Pennsylvania. SOURCE: Adapted from ORSANCO; available on-line at

Rivers System of the United States National Park Service.1 One of its tributaries, French Creek, is widely known for its diverse natural history, including aquatic species found in this region when European settlement arrived in the mid-eighteenth century.

The Monongahela River drains 7,340 square miles of Maryland, Pennsylvania, and West Virginia (see Figure 2-2). The river rises in the Allegheny Mountains and flows generally northward from Fairmont, West Virginia, through mountainous terrain, farming communities, urban and industrial areas, and coal fields to its confluence with the Allegheny River in Pittsburgh. Over its length of approximately 130 miles, the river is spanned by several locks and dams to facilitate barge traffic. Upstream, a network of dams constructed and operated by the Corps of Engineers since the late 1930s help enhance low flows.


See and for further information about the program and the Allegheny River’s designation, respectively.

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