Which lot do you pull into when you want an hour on the canal? This season that choice matters more than the trail itself. The C&O Canal towpath is open daily from sunrise to sunset, all year. Almost all of this winter's repair work sits beside it instead: in the parking areas, on the roads that lead to them, and along the 54-mile Potomac Interceptor sewer line that runs parallel to the canal.
Between Lock 10 and Rileys Lock, the familiar access points are each in a different state. Walking upriver one at a time shows where the friction is.
Where Each Access Point Stands
This table follows the National Park Service's current conditions page, last updated November 5, plus DC Water's project notices.
| Access point | Mile | Parking | What's going on |
|---|---|---|---|
| Lock 10 | 8.8 | Open | Long-term Potomac Interceptor rehabilitation nearby. Expect short towpath delays when equipment moves |
| Carderock | 10.5 | Open, Lot 1 reduced | Tunnel down to one alternating lane. Restrooms closed, portable toilets on site |
| Great Falls Tavern | 14.3 | Open | Entrance road open. Visitor center goes to winter hours December 1 |
| Swains Lock | 16.7 | Closed | Flood-damage repairs. Lockhouse 21 still reachable |
| Pennyfield Lock | 19.6 | Limited | Emergency sewer repair at Muddy Branch. Possible delays on Pennyfield Lock Road |
| Rileys Lock | 22.8 | Open | Lockhouse tours on weekends through December 12 |
Mile 8.8: Lock 10 and the Pipe Beneath the Parkway
The work started here. On January 19, 2026, the Potomac Interceptor failed along the Clara Barton Parkway in Cabin John. DC Water then expanded inspections across the whole line, using video, LiDAR to measure wall thickness, and sonar to find blockages. DC Water reports that the last overflow reached the river on February 8 and that emergency repairs were done, with flow restored, by March 14. Since then the work has been long-term rehabilitation of more than 2,700 linear feet of pipe. In August, Montgomery County lifted all remaining shoreline health advisories, as Bethesda Magazine reported. DC Water's October 7 expanded sampling found river results within the normal range.
The park's conditions page still carries a caution about the Interceptor near Lock 10. It warns of possible odors and lists DC Water's 24-hour Command Center at 202-612-3400. The Lock 10 lot and towpath are open. Visitors may see brief delays while equipment moves, and flaggers are posted.
The repair from Lock 14 down to Lock 10 is slip-lining: fiberglass-reinforced pipe is fed inside the old pipe. The bypass piping runs along the Clara Barton Parkway shoulder, and NPS describes the work site as outside the towpath and other main visitor areas, with no formal closures planned. DC Water's September 23 presentation to the Brookmont Civic League put the permanent repair schedule at April 2026 through January 2027.
Getting to the canal by car is the bigger disruption. DC Water is closing one lane of the Clara Barton Parkway at the Maryland–DC border for another emergency slip-lining job on about 400 feet of pipe. Through Friday, November 20, one lane can close daily from 10 a.m. to 2 p.m., with flaggers alternating traffic. More closures are possible as needed through December 23. A late-morning drive in on the parkway can hit that work zone. A sunrise walk avoids it.
Mile 10.5: Carderock, Open With Asterisks
The next lot upriver is the first one where construction staging takes up spaces. Carderock's lots are open, but Lot 1 has reduced capacity for contractor staging. The tunnel has run as one alternating lane since July 27. The restrooms are closed for emergency repairs, and portable toilets are on site. The tunnel job covers concrete and drainage repairs at Carderock. Towpath through-traffic is meant to stay open the whole time. The park's own schedule for this work said summer 2026, and the lane restriction has outlasted it.
Mile 14.3: Great Falls Tavern Takes the Load
Above Carderock, the lots thin out. That makes Great Falls the steadiest base on this stretch for the rest of the year. The entrance road on MacArthur Boulevard is open, and so are the parking lot, restrooms, Great Falls Overlook, Olmsted Island Boardwalk, Gold Mine Loop and River Trail. All three sections of the Billy Goat Trail are listed open. The same flood-repair contract that closed Swains also covers this road. During construction, it allows intermittent single-lane closures at the entrance, which can slow traffic coming in and going out.
The Tavern's hours shift on December 1. Until then the visitor center is open Sunday and Wednesday through Saturday, 9 a.m. to 4 p.m. From December 1 through February 28 it opens Sunday and Thursday through Saturday, 9 a.m. to 4 p.m., and closes Monday through Wednesday. It is also closed on Thanksgiving, Christmas Day and New Year's Day. Canal boat rides are done for the season.
Miles 16.7 to 19.6: Swains and Pennyfield, Where the Detours Stack
This is the stretch where the choice of lot matters most, because the two neighboring access points are both affected at once.
The Swains Lock lot closed on October 13 for what the park called "several weeks," and NPS still listed it closed on November 5. The repairs date back to a flash flood on July 8, 2019. Crews are removing the damaged timber retaining wall around the lot and replacing it with a seeded embankment. They are also rebuilding shoulders, adding drylaid stone armoring and a new drainage pipe, and stabilizing stream beds. Federal Highway Administration emergency road funds pay for the work. NPS sends towpath parkers to Pennyfield upstream or Great Falls downstream.
Pennyfield has its own work. DC Water is rehabilitating about 1,700 feet of 60-inch Interceptor pipe at Muddy Branch near Lock 22. This section carries about six million gallons of wastewater on a typical dry day, upstream of drinking water intakes on the river. DC Water says there is no emergency, overflow, or effect on drinking water at this site. A temporary bypass has carried flow around the repair area since July 9. At an October 7 update for the Tobytown community, DC Water said construction should finish in December and site restoration should follow in January, weather and construction allowing. Crews work from 7 a.m. to 5 p.m. Pennyfield parking may be short because of equipment staging, temporary trail closures may be signed, and NPS flags possible delays on Pennyfield Lock Road.
The parking lot that NPS names as the upstream fallback for Swains is a construction staging site until at least December. For a walk toward Swains, the lot without a construction caveat is Great Falls, 2.4 miles downriver.
Overnight guests are less affected than day visitors. Lockhouse 21 at Swains stays reachable during the lot closure. The C&O Canal Trust's Canal Quarters program rents Lockhouse 21 from November through April for $135 a night plus an $80 one-time cleaning fee. Lockhouse 22 at Pennyfield rents for $75 a night. Lockhouse 22 is the rustic one, with no heat, electricity or indoor plumbing, and its nearby water pump is shut off for winter.
Mile 22.8: Rileys Lock Before the Tours End
At the top of the Potomac stretch, the Seneca Aqueduct and the Rileys Lock lot are open. Riley's Lockhouse at Lock 24 has free guided tours on Saturdays and Sundays at 1 p.m., with public hours from 1 to 4 p.m., through December 12. Girl Scouts lead the tours and give Victorian-era demonstrations, weather permitting. The last tour day is Saturday, December 12.
A Drained Canal, With One Exception
The canal itself has changed too. Each fall the park drains the watered sections to protect the stone masonry from freezing, as the canal company did in its operating years. On November 5, every section from Lock 17 through Lock 23 was drained. That covers the canal alongside Great Falls, Swains and Pennyfield. Widewater still held water.
Widewater is also where Nature Forward has scheduled its December outings on this stretch. The Midweek Meander Along the Canal at Widewater, led by Stephanie Mason, runs December 2 from 10 a.m. to 12:30 p.m. The Solstice Celebration Hike on December 18, led by Genevieve Wall and Stephanie Mason, runs from noon to 4:30 p.m. It starts at Widewater, goes upriver to the Great Falls Overlook and comes back, nearly four miles in all. Details and registration are on Nature Forward's program page.
One more seasonal change matters for longer outings. Around mid-November the park turns off water faucets in its camping areas until spring. The November 5 list still showed potable water on at Lock 10, Carderock, Anglers, the Great Falls Tavern restrooms and the Swains Lockhouse. The faucets at the Swains hiker-biker site and Rileys were already off. The park's standing advice is to carry your own water.
Before you head out, the park's conditions page and DC Water's Pennyfield Lock project page have the current status. For questions about Swains or the entrance road, park headquarters is at 301-739-4200.
A home near River Road or MacArthur Boulevard comes with this kind of local knowledge: which roads slow down at midday and which lot to use while Swains is closed. The Schuman Team has worked in Potomac for more than four decades. If you'd like to know what your home near the canal is worth this season, we're glad to walk you through it. Get Your Home's Value.
