Locks on the C&O Canal

The Locks on the Chesapeake and Ohio Canal, located in Maryland, West Virginia, and Washington, D.C. of the United States, were of three types: lift locks; river locks; and guard, or inlet, locks.

They were numbered from 1 to 75, including two locks with fractional numbers (63⅓ and 64⅔) and none numbered 65. There is also the Tidewater Lock, sometimes called Lock 0, lock at the downstream end of the canal in Washington, D.C., where Rock Creek flows into the Potomac River.

The fractionally numbering arose because locks 70-75 were completed in 1842, before locks 62 and 66. It was found that the level of the canal between locks 62 and 66 could be raised in three steps instead of four. So the additional locks through there were numbered 1⅓ steps apart (62, 63⅓, 64⅔ and 66) so that the other locks, already completed, did not have to be renumbered.

While the "Frequently Asked Questions" website published by the National Park Service states that it takes about 10 minutes for a boat to lock through, experiments done in the 1830s show that it was possible for a boat to go through in 2½ minutes, although 3 minutes was their average. In 1897 it was shown that steamboats took 5 to 7 minutes to lock through whether going upstream or downstream (respectively).

Since these were locks to regulate water coming into the canal, they are frequently called inlet locks. At the slackwaters (particularly at Big Slackwater and Little Slackwater) they allowed boats to reenter the canal from the slackwater. There is no guard lock #7, since Dam #7 was proposed to be around mile 164 near the mouth of South Branch, but it was never built. A steam pump was later put where this dam would have been in 1856. In 1872, a new steam pump was put 10 miles upstream at mile 174.2, and gave about 24 cubic feet per second of water.

The first guard lock was made of structures from George Washington's Potomac Company Little Falls skirting canal, and were repurposed for the C&O.

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