The Canal Through Potomac Is Open This Fall. The Parking Lots Are Where the Work Is.

The National Park Service's current conditions page for the C&O Canal was last updated October 9, 2026. It lists the towpath as open at every access point between Lock 10 and Rileys Lock. That covers Carderock, Anglers, all three sections of the Billy Goat Trail, the Olmsted Island boardwalk and the Seneca Aqueduct.

The same page also lists a sewer overflow caution, a tunnel lane closure, closed restrooms, a lot with reduced capacity, and a parking closure at Swains Lock that starts October 13. None of this work is on the trail itself. It's happening under the parkway, behind an old retaining wall and inside a road tunnel, which means it lands on the places where you leave your car. On this stretch of the canal this fall, picking a start point is the decision that matters.

A Sewer Main Under the Parkway

The biggest project here belongs to DC Water, not the park. The Potomac Interceptor is a sewer line that runs through the park. According to DC Water, a section of it collapsed along Clara Barton Parkway on January 19, 2026, and wastewater overflowed into the park. The last overflow to reach the Potomac was on February 8. Emergency repairs were done and full flow restored by March 14.

That fixed the immediate problem but didn't end the work. DC Water is now rehabilitating about 2,700 feet of pipe between the I-495 interchange and Lock 10. The project page says construction is expected to run through February 2027, with one lane closed and a 30 mph speed limit in the work zone. At Lock 10, NPS lists the lot and towpath as open but warns of short delays on the towpath while equipment moves, and possible odors.

As of October 9, the park's caution still says DC Water is managing a sanitary sewer overflow near Lock 10. The river itself has a separate report. In an October 7 release, the utility said expanded testing found the river healthy and within normal ranges, with no current signs of harm from the January overflow.

The same pipe causes the problem six miles upstream. At Pennyfield Lock, DC Water is repairing about 1,700 feet of 60-inch pipe at Muddy Branch. Inspections there found worn concrete, corrosion and exposed reinforcement. WTOP reported the June 15 start and the above-ground bypass that keeps wastewater moving during the work. By July 27, DC Water said it had finished lining the most critical 175-foot section and expected to start slip-lining the rest in late August.

The original schedule had construction ending by late September. As of October 9, NPS still lists repairs near Lock 22 and warns of possible delays on Pennyfield Lock Road. DC Water's project page says work runs 7 a.m. to 5 p.m. and that equipment staging may limit parking at Pennyfield. No newer end date has been published.

A 2019 Storm Still Being Repaired

That matters because Pennyfield is one of the two lots the park recommends while Swains Lock is closed.

The Swains closure traces back to the flash flood of July 8, 2019. According to the NPS project page, the flood eroded the Great Falls entrance road embankments and left drop-offs along the shoulders. At Swains, the contract removes a damaged timber retaining wall and replaces it with a filled, seeded soil embankment. The page names Pennyfield Lock at mile 19.6 and Great Falls at mile 14.3 as alternate towpath parking while the Swains lot is closed. The conditions page has the closure starting October 13 and lasting "for several weeks."

The C&O Canal Trust adds two details the park leaves out. Its notice says the Maryland State Highway Administration is making urgent repairs to the Swains Lock lot starting the week of October 12, with completion estimated around the end of October.

Lockhouse 21 at 10700 Swains Lock Road is caught in the middle. The Swains family owned the property for more than a century before donating the building to the park in 2005. Today it's an overnight rental in the Canal Quarters program, furnished to evoke the 1910s, when the canal was still running. The Trust has blocked some dates on the reservation calendar and emailed guests whose stays are affected.

The same contract covers the Great Falls entrance road. NPS says the road stays open, with intermittent single-lane closures and possible delays while crews work on what lies under the pavement. Repaving is a separate project that is still being planned.

Carderock, Where the Finish Date Has Passed

Downstream at mile 10.5, the work is in the tunnel that carries traffic into the Carderock recreation area. NPS is repairing erosion damage and deteriorated concrete there. The plans include masonry work, earthwork and repaving the approaches. An alternating one-lane closure started July 27, 2026. The project page gives a schedule ending in "Summer 2026." As of October 9 the closure is still listed, so the summer estimate no longer holds.

Parking Lot 1 is open with reduced capacity because the contractor is staging there. The restrooms are closed for emergency repairs with no reopening date, and portable toilets are on site. The Carderock Pavilion and the other lots are open.

Two Lots Without Construction

Two neighboring access points on this stretch have no construction affecting their parking lots.

At Anglers, mile 12.2, the lots and restrooms are open and the water faucet is still on. From there, Billy Goat Trail Sections A, B and C are all open. Section A is the one most likely to close. NPS normally shuts it when the Little Falls gauge reaches 5 feet and reopens it at 4.8 feet, and it can close at lower readings in some conditions. The Great Falls Tavern Visitor Center takes calls about closures at 301-739-4200 during business hours.

At Great Falls Tavern, mile 14.3, the parking lot, restrooms, Great Falls Overlook, Olmsted Island boardwalk, Gold Mine Loop and River Trail are all open. The canal boat rides have closed for the season. In the Gold Mine Tract, between MacArthur Boulevard and Berma Road, hikers must stay on designated trails. The visitor center's hours change twice before the new year:

• Now through November 30: 9 a.m. to 4 p.m., Wednesday through Sunday. Closed Monday and Tuesday.
• December 1 through February 28: 9 a.m. to 4 p.m., Thursday through Sunday. Closed Monday through Wednesday.
• Holiday closures: November 26, December 24 and December 25, 2026.

With Swains closed, Great Falls Tavern is the park's other recommended alternate, and the occasional single-lane delay on the entrance road is the only construction a driver will meet there.

Reading the Stretch Mile by Mile

Here is how the access points compare as of the October 9 update, listed from downstream to upstream:

The canal is also changing as the season turns. NPS drains the watered sections every fall to protect the stone masonry from freezing. As of the September 28 water-level update, the stretch from Lock 17 through Lock 22 was still watered and the section between Locks 22 and 23 had been drained. Water faucets in the park's camping areas usually shut off around mid-November. The Swains Lockhouse faucet runs on the same municipal water as the lockhouse and is listed as potable.

The towpath runs all the way from here to the Georgetown end of the canal, so this list covers only Potomac's share of a much longer park. The park updates the conditions page as work moves forward. Swains could reopen at the end of October, Pennyfield's crews could finish any week, and the Carderock tunnel is already past its posted schedule.

Some modern homes in Potomac sit a short drive from these lots. If you own one and are thinking about what it's worth, listModern can tell you how design-minded buyers value a modern house this close to the towpath.