A Lift Lock

When a river such as the Potomac was too swift or shallow for navigation, shippers built canals with lift locks along the river course. The C & O Canal consists of flat stretches of water connected by lift locks, and the use of locks enabled the canal to match the river’s gradient. Water was permitted to flow into or out of a lock by opening or closing a paddle at the bottom of each lock gate. For a boat heading downstream, the boat enters the lock, the mules are unhitched and led downstream, the lock gates are closed, the downstream paddles are opened so water flows out and the boat is lowered, and when water levels are equal, the mules are hitched again, the gates are opened, and the boat continues downstream.

Potomac, Maryland · United States