The Monongahela River ("The Mon") forms at Fairmont, where the West Fork and Tygart Valley rivers merge. It flows 128 miles north to Pittsburgh, where it joins the Allegheny River to form the mighty Ohio River.

Long ago, a glacier blocked an ancient river here, creating a huge lake called Lake Monongahela. Today, the river is entirely navigable thanks to a system of locks and dams.

Early settlers used flatboats and later keelboats to move cargo, including Monongahela rye whiskey (which helped spark the Whiskey Rebellion of 1794). The Monongahela was the first river in the United States to be fully controlled for navigation by a system of dams, completed in the early 1900s.

Flooding was a major problem. After huge flooding in 1907, the public realized that timbering was making the floods worse. This led to the creation of the Monongahela National Forest in West Virginia to protect the watersheds and control future floods.