Potomac's Towpath Stayed Open All Year. The Canal Beside It Is Still Being Rebuilt.

Between Lock 10 and Lock 14, the C&O Canal is a construction site with a footpath running alongside it. Crews are rebuilding the canal's clay liner, the waterproof seal that keeps water in the channel. They are also restoring the channel's shape and slope and rebuilding its wooden lock gates. Through all of it, the towpath has stayed open to walkers, runners and cyclists.

That pattern holds along the whole Potomac stretch of the canal this winter. The towpath itself is clear from Lock 10 up to Pennyfield Lock. The work is happening at the edges, in parking lots, parkway lanes, a road tunnel and a boat ramp. On a November or December weekend, the question that matters is which trailhead can get you onto the path.

What January did to the canal, and what it spared

On January 19, 2026, a 72-inch section of DC Water's Potomac Interceptor sewer collapsed along the Clara Barton Parkway in Cabin John and spilled more than 200 million gallons of wastewater. DC Water says the last overflow reached the river on February 8. The emergency repair was finished, with full flow restored, on March 14. The day after the collapse, Bethesda Magazine reported DC Water's statement that the towpath had not been breached and was still open to the public.

The canal took the hit instead. During the emergency repairs, the stretch between Locks 10 and 14 served as a temporary bypass and carried nearly two billion gallons of wastewater. That is close to ten times the volume that spilled. In its October 30 announcement, DC Water said crews had spent months removing sludge and had dug out 8,500 tons of contaminated soil from that stretch. Testing confirmed bacteria levels in the soil were safe, and restoration began that day.

DC Water is restoring the canal to National Park Service specifications. In the same announcement, it said: "When the work is done, the canal will be in better condition than before the incident."

The pipe work is continuing too. Crews are building a bypass system of four parallel pipes, each more than 2,700 feet long, sized for 120 million gallons a day. Once the bypass is ready, they will slipline the old sewer, which means inserting a new pipe inside the existing one. DC Water expects that work to finish "in the spring."

The closures moved from the towpath to the parkway

The National Park Service fenced off the work zone, not the path. In February, it closed the right lane of the Clara Barton Parkway and the wooded area between the parkway and the canal, from the Lock 10 parking lot north to Lock 14. At that point it expected to restore the area by April 30, 2026. A newer order, Closure Order 26-04, signed September 24, 2026, extends the closure through April 30, 2027. It covers 3,500 feet of the parkway's right travel lane and the managed land beside it. The towpath, the Lock 10 parking lot and the access trail all stay open.

There are two more traffic changes on the parkway this winter:

• DC Water's November 3 traffic advisory calls for periodic one-lane closures at the Maryland–DC border from November 4 through December 23, 2026. Work runs from 10 a.m. to 2 p.m. and from 8 p.m. to 4 a.m., with flaggers keeping one lane open.
• DC Water's Rock Run project near Lock 10 runs from late summer 2026 through February 2027. It keeps one lane closed and sets a 30-mph speed limit on the inbound parkway before the I-495 ramp toward Lock 10.

If you head out for a midday walk from Lock 10, the 10-to-2 work window falls right on your drive.

Trailhead by trailhead, heading upstream

The National Park Service updates its current park conditions page as things change, and the version dated November 3, 2026 is the baseline below. Each stop has a different issue, and each one shifts walkers to another stop.

1. Lock 10, milepost 8.8. The parking lot and towpath are open. NPS warns of short towpath delays when equipment is moved, and visitors may notice odors from the Interceptor work. The NPS planning page for the Lock 10 to Lock 14 repairs says the site sits outside traditional visitor areas such as the towpath and needs no formal area closures.
2. Carderock, milepost 10.5. The Carderock Pavilion is open. The tunnel has had an alternating one-lane closure since July 27, 2026, and Parking Lot 1 is open with reduced capacity because the contractor is staging there. The restrooms are closed for emergency repairs, and portable toilets are available. The project covers erosion and concrete damage at the Carderock culvert, plus wingwall, approach-paving and sign repairs.
3. Great Falls Tavern, milepost 14.3. This is the most complete stop on the Potomac stretch. The visitor center, entrance road, parking lot, restrooms, Great Falls Overlook and Olmsted Island Boardwalk are open, along with the Gold Mine Loop and River Trail. All three sections of the Billy Goat Trail are listed open. The entrance road on MacArthur Boulevard is open, but repairs may bring intermittent single-lane closures.
4. Swains Lock, milepost 16.7. The parking lot was scheduled to close for construction on October 13 for "several weeks." Lockhouse 21 is still accessible, and the hiker-biker campground is open. NPS points walkers to Great Falls or Pennyfield Lock as the nearest places to park.
5. Pennyfield Lock, milepost 19.6. Parking and access are open, though deliveries of construction equipment and pipe can cause brief disruptions. NPS also warns of delays on Pennyfield Lock Road. Boat trailers cannot use the ramp during the project. Kayakers and other paddlers launching without a trailer still have access.

The Swains Lock closure has nothing to do with the sewer. It is part of NPS repairs to flash-flood damage from heavy rain on July 8, 2019. The storm eroded embankments that threaten to undermine the Great Falls Entrance Road, scoured drop-offs into the shoulders, and damaged the timber retaining wall at Swains Lock. Crews are replacing that wall with a filled, topsoiled embankment. The work began in phases in 2025 and runs through 2026, depending on weather.

The Pennyfield work is a preventive repair, not a cleanup after a spill. Inspections found worn concrete, corrosion and exposed reinforcement along about 1,700 feet of pipe that carries roughly six million gallons on a dry-weather day. Crews finished lining the most urgent 175-foot section on July 27. At an October 7 meeting with the Tobytown community, DC Water said it now expects to finish the work in December and restore the site in January, depending on weather and any other construction problems.

That leaves Great Falls handling more walkers. With Swains Lock's lot closed and Carderock's Lot 1 at reduced capacity, more people start their walks at the Great Falls Tavern lot. The entrance fees there, as NPS lists them, are $20 per private vehicle, $15 per motorcycle and $10 per person arriving on foot or by bicycle for ages 16 and up. The park does not accept cash.

The winter calendar on top of the construction

The usual seasonal changes are arriving at the same time as the construction, and some happen every year regardless of the repairs. Each fall, NPS drains, or "de-waters," the canal to protect the stone masonry from freezing, and water usually returns in early spring. As of NPS's October 14 update, the canal still held water between Locks 17 and 21 near Great Falls and was drained from Lock 21 up through Lock 23. The Great Falls canal boat rides are closed for the season.

The visitor center change matters most for guests. Its posted hours are 9 a.m. to 4 p.m. on Sunday and Wednesday through Saturday. From December 1 through February 28, it closes Monday through Wednesday and opens Thursday through Sunday. Wednesday visits to the tavern stop working after November 30.

Weather can still close the river side of the Great Falls area. Section A of the Billy Goat Trail usually closes when the Little Falls gauge reaches 5 feet and reopens when it falls to 4.8 feet. NPS says it can close at lower levels in some conditions and lists the visitor center at 301-739-4200 for current closures.

The towpath is the one route on this stretch with no closure dates attached to it. The parkway lanes, the lots at Swains Lock and Carderock, the trailer ramp at Pennyfield and the visitor center's weekday hours all change on their own schedules this winter. A walk out of Great Falls Tavern on a Thursday through Sunday involves the fewest of them.

At Cox & Cox Group, we follow the details that shape a Potomac weekend, from the parking lot at Lock 10 to the Thursday hours at Great Falls Tavern. If you are weighing a move to a home near the canal or have questions about life along the River Road corridor, Contact Us — Let's Solve Your Home Needs.