The Monongahela River is a river of the eastern United States of America. It is one of the largest rivers in the US to flow in a generally northerly direction.

It rises in the Allegheny Mountains from the confluence of two lesser streams near Fairmont in Marion County, West Virginia, not far from the headwaters of the Potomac River which flows the opposite direction, towards the Atlantic Ocean. It flows north into Pennsylvania where it unites with the Allegheny River to form the Ohio River at Pittsburgh.

The Monongahela has been heavily used by industry, and several US Steel plants, including the Homestead Works, were built along its banks.

Two ships in the United States Navy have been named Monongahela for the river.

See also

• List of Pennsylvania rivers
• List of West Virginia rivers