Chesapeake and Ohio Canal National Historical Park | TIDE LOCK

C & O Canal's Tide Lock at the confluence of Rock Creek and the Potomac River

C & O Canal’s Tide Lock at the confluence of Rock Creek and Potomac River


The Tide Lock is located in Georgetown next to the Thompson Boat Center. See the Locks and Lockhouses web page for an interactive location map.


Lock 1 is not the first lock on the Chesapeake and Ohio Canal. The official 0 Mile point is at the confluence of Rock Creek and the Potomac River. When the canal was in operation, Rock Creek was dammed at the mouth of the Potomac to create a pool of water called the Mole. This allowed space for the canal boats to line up before entering the first lock. To get around the dam, a tide lock (aka inlet lock) was built. Boats coming from the Potomac River passed through the lock to enter the Mole, and boats finishing their journey on the canal exited through the lock to get back on the Potomac River. Remnants of the tide lock still exists on the east side of the Thompson Boat Center building, a National Park affiliated boat and bike rental shop in Georgetown.

The easiest way to get to the Tide Lock is to park at the Thompson Boat Center parking lot on Virginia Avenue and walk from there. However, if you are in Georgetown and visiting Locks 1 through 4, you can also reach it via a short walk from Lock 1. Take the brick sidewalk on the left side of the lock and walk downstream—away from Lock 2—until you reach the paved Rock Creek Trail. Take a right on the trail to head towards the Potomac River.

The Rock Creek Trail is on the east side of Rock Creek, and you’ll need to get to the other side. To do so, when you reach Virginia Avenue, turn right and continue past the parking lot for the Thompson Boat Center. Just beyond the parking lot is a bridge that spans Rock Creek, and once across it you will be at the boat center building, but on the opposite side from the Tide Lock. Just walk along the paved path between the building and the dock and you’ll run smack into the Tide Lock.

Lock gate across the mouth of the C & O Canal's Tide Lock at the Potomac River

Lock gate across the mouth of the C & O Canal’s Tide Lock at the Potomac River

In the photo below, the Tide Lock is in the foreground and the mouth of Rock Creek is in the background. When in operation, a dam would have spanned the mouth of the creek. In the second photo below, you can see the mouth of Rock Creek and remnants of the old dam.

Tide Lock at Mile 0 on the Chesapeake and Ohio Canal

Tide Lock at Mile 0 on the Chesapeake and Ohio Canal

Confluence of Rock Creek and Potomac River where a dam once stood

Confluence of Rock Creek and Potomac River where a dam once stood

After entering the Tide Lock from the Potomac, boats traveled a short distance through the lock channel before hitting the Mole. Today the channel is filled in with vegetation and other debris, but water still flows through it. A footbridge spans the channel, allowing you to get on either side of the lock.

View of the C & O Canal Tide Lock at Mile 0 facing the Potomac River

View of the C & O Canal Tide Lock at Mile 0 facing the Potomac River

Tide Lock at Mile 0 on the C & O Canal connects to Rock Creek

Tide Lock at Mile 0 on the C & O Canal connects to Rock Creek

There was no towpath from the Potomac River up to Lock 1, so boatman had to use poles to move upstream. If you walked to the Tide Lock from Lock 1, the towpath started about where you met up with the Rock Creek Trail. From there to 29th Street, the original towpath was on the opposite side of the canal from the present day sidewalk. At 29th Street the mules crossed over the canal and then headed upstream to Lock 2. From 29th Street to the end of the canal in Cumberland, Maryland, the current towpath follows the original route with very few exceptions. The only difference is that in Georgetown it is now a brick sidewalk instead of a dirt path.

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Last updated on January 16, 2022
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