The major U.S. river system that has headwaters in the Appalachian Mountains is the Ohio River.

The Ohio River begins at the confluence of the Allegheny and Monongahela Rivers in Pennsylvania, which are both fed by tributaries originating in the Appalachian region. The Ohio River flows through several states before joining the Mississippi River, serving as an important waterway for transportation, commerce, and recreation in the region. Its headwaters in the Appalachian Mountains highlight the river's connection to this significant geographical area.