A river rising in north-central Pennsylvania and flowing approximately 523 km (325 mi) northwest into New York then weaving its way southwest into Pennsylvania again, where it joins the Monongahela River at Pittsburgh to form the Ohio River at The Point.

As the river meets its final destination in Pittsburgh, it is somewhat interesting to note that part of the Pittsburgh Regatta takes place on the Allegheny. Steel mills, coal transportation, and other Industrial Age industry relied on the river for rapid transportation of materials. The river is still used today for the same purposes, although to a much lesser extent.

Also, the Allegheny River is somewhat cleaner than the Mon.