Chesapeake and Ohio Canal National Historical Park | DAM 3 RUINS AND INLET LOCK

Ruins of Dam 3 at Mile 62.3 on the Chesapeake and Ohio Canal towpath

Ruins of Dam 3 at Mile 62.3 on the Chesapeake and Ohio Canal towpath


The ruins of Dam 3 and an inlet lock are located just north of Harpers Ferry at Mile 62.3 on the C&O Canal towpath. It cannot be accessed by vehicle, so reaching it requires hiking or biking 2.6 miles (one way) downstream from the Dargan Bend Boat Ramp parking lot. See the Locks and Lockhouses web page for an interactive location map.


The current layout of the Chesapeake and Ohio Canal between Locks 34, 35, and 36 is very confusing. If you are traveling upstream from Lock 34, just before reaching Lock 35 the towpath veers from the canal onto a service road and heads towards the Potomac River, completely bypassing the lock. You can see the lock, but you can’t get to it.

If you are heading downstream from Lock 37, the towpath takes an unexpected sharp right-hand turn towards the Potomac River—once again on this service road—when you reach Lock 36. It is obvious that the canal continues straight ahead towards Lock 35 (less than a tenth of a mile away). In fact, if you want to see Lock 35 you must ignore this detour and continue along the original towpath, which is now a wide, grassy trail. You cannot go farther, so after checking it out, return to Lock 36 and take the detour.

Path from Lock 36 to Lock 35 in Chesapeake and Ohio Canal National Historical Park

Path from Lock 36 to Lock 35 in Chesapeake and Ohio Canal National Historical Park

What has happened is that Lock 35 and an inlet lock just above Dam 3 (a stone’s throw away on the Potomac River) merge together in a V-shape, with the point of the V aiming downstream. The original towpath runs down the middle of the V and eventually comes to the point. With nowhere to go, it had to cross over either the inlet lock or Lock 35 via a footbridge to continue alongside the canal—it crossed over the inlet lock. The bridge is no longer there, and for whatever reason, the National Park Service chose not to rebuild it, instead opting for the service road detour.

Dam 3 caused the Potomac River to pool behind it, and this ready-made water surplus was funneled into the canal through the inlet lock, which could be opened and closed to regulate the flow. This was the source of water for the canal from here all the way to Seneca. The inlet lock also let boats coming from West Virginia enter into the canal, thus drumming up additional business.

Today the inlet lock is plugged with stone at both the river end and the canal end to keep the waters of the Potomac out of the canal (the photo below shows the canal-end plug). The service road crosses the inlet lock over the river-end plug, making it the modern substitute for the original bridge. Why the National Park Service didn’t make the crossing over the canal-end plug and have the towpath continue on its original course is beyond me. My only guess is that these plugs were put in before the C&O Canal became a National Park unit and that the river-end plug was wider, thus allowing more room for hikers and bikers. But that’s just a guess.

Layout of the Inlet Lock and Lock 35 in Chesapeake and Ohio Canal National Historical Park

Layout of the Inlet Lock and Lock 35 in Chesapeake and Ohio Canal National Historical Park

As you follow the detour you will see a short path that leads down to the Potomac River where you can view the ruins of Dam 3. The origin of the dam stems all the way back to 1799 when it was built to divert water to the Harpers Ferry Arsenal, though it didn’t work very well. In 1832, the C&O Canal engineers took the existing structure and modified it for canal use. Not much of it remains today, and you must look carefully to differentiate the hand-cut stones from natural rocks in the river. The dam was built in a zigzag pattern, so do not expect a linear line of hand-cut stones (see photo at the top of this page).

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Last updated on June 19, 2024
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