Potomac River

The Great Falls of the Potomac rendered the upper reaches of the river unnavigable.

The Potomac River is a river in the eastern United States. It forms the boundary between the states of Virginia and Maryland. Washington DC lies on its northern bank. Alexandria, Virginia and Arlington, Virginia are cities on its southern bank.

Ocean going vessels could navigate on the lower reaches of the Potomac, in the 18th century, and quays and warehouses were built in 18th century Alexandria.

The Great Falls of the Potomac, and other navigational impediments, rendered the upper reaches unnavigable.