At Swains Lock, the canal is split down the middle. Upstream of Lock 21, toward Pennyfield and Seneca, the prism has been drained for the season. Downstream, from Lock 21 back past Great Falls Tavern to Lock 17, the water is still in. The National Park Service's October 14 conditions update listed Locks 21–22 and 22–23 as dewatered, while Locks 17–19, 19–20, 20–21 and Widewater were all still watered.
Draining the canal every fall is normal. The park does it to protect the stone masonry from freezing, and the C&O Canal Company did the same thing when the canal was still carrying boats. Water usually returns in early spring.
This year's version runs longer than usual. Through November and into December, each Potomac entrance to the towpath is on its own schedule, set by repair contracts, sewer work and seasonal hours. The towpath is open the whole way. Your choice of trailhead is what decides whether you find parking, a restroom and a visitor center when you get there.
Four Entrances, Four Different Schedules
Here is where each Potomac access point stood in late October, using NPS mileposts.
| Access point | Milepost | Parking | Restrooms | What's going on |
|---|---|---|---|---|
| Carderock | 10.5 | Open; Lot 1 at reduced capacity | Closed for emergency repairs; portable toilets on site | Carderock Tunnel down to alternating one-lane traffic since July 27 |
| Great Falls Tavern | 14.3 | Open | Open | Visitor center open; entrance road open with possible single-lane flagging |
| Swains Lock | 16.7 | Closed since October 13 | Lockhouse water stays potable | Repairs to the embankment and retaining wall |
| Pennyfield Lock | 19.6 | Parking may be limited | Not listed | DC Water sewer repairs expected to finish in December |
At Carderock, a contractor is staging in Lot 1 for a tunnel project that also covers tunnels at Four Locks and McCoys Ferry, much farther upriver. The Carderock Pavilion and the parking lots are open, but the permanent restrooms are not. The NPS project page still gives an anticipated schedule ending in summer 2026. The one-lane closure only started in late July, so the park's live conditions page is the better guide.
Why Swains Lock's Lot Is Fenced Off
The Swains closure traces back to one storm. On July 8, 2019, a burst of intense rain sent flash flooding through the Great Falls area. It eroded the embankments along the Great Falls Entrance Road on MacArthur Boulevard and damaged the timber retaining wall around the Swains Lock parking area. According to the NPS project page for the repairs, crews at Swains are removing that wall and replacing it with an embankment of fill and seeded topsoil. Along the entrance road, the work covers stone "rockery" armoring walls, rebuilt shoulders, a new drainage pipe and stabilized stream beds. The money comes from the Federal Highway Administration's Emergency Relief for Federally Owned Roads program.
The two agencies give different reopening estimates. NPS says the lot closed beginning October 13 and will stay closed "for several weeks." The C&O Canal Trust, which manages the overnight lockhouse at Swains, puts restored parking access "around the end of October." That leaves the lot's status this week uncertain. NPS names the fallbacks: Pennyfield Lock is the nearest parking upstream and Great Falls the nearest downstream.
Pennyfield won't be fully back to normal for a while. DC Water's project page says that at an October 7 meeting with the Tobytown community, it moved completion of its emergency Potomac Interceptor repairs to December, with restoration of the area in January, depending on weather. This summer the work was expected to wrap up in September, as MoCo Show reported in June. In July, crews put a geopolymer lining inside a 175-foot concrete-encased section of the pipe. The next phase, slip lining a new pipe inside the old one, was set to start in late August. NPS warns of possible delays on Pennyfield Lock Road.
Put those two together and the free entrances on either side of Great Falls are both affected through at least November. With Swains closed, a walk from Pennyfield to Swains and back has no parking at the Swains end. Starting from Carderock means a one-lane tunnel, a smaller lot and portable toilets.
Great Falls Is the One Entrance With Everything Working, and It Charges
Great Falls Tavern is the only Potomac entrance where every facility and trail on the NPS list reads open. The canal boat rides are done for the season, but everything else is running, including the visitor center, parking, restrooms, the Great Falls Overlook and Olmsted Island Boardwalk, the Gold Mine Loop, the River Trail, and Sections A, B and C of the Billy Goat Trail.
It is also the only part of the C&O Canal National Historical Park that charges admission. The NPS fee page lists $20 per private vehicle, $15 per motorcycle, and $10 per person 16 and older arriving on foot or by bike. Visitors under 16 get in free, and the $35 annual park pass is accepted. Payment is card only. The page was last updated in 2025, so check current rates before you go.
Expect some friction at the gate. The entrance road is open, but NPS says intermittent single-lane flagging can slow traffic in and out while the embankment work continues. NPS also notes that a separate, larger repaving project for the road is still in design.
Water is another reason Great Falls holds up through the cold months. Around mid-November, NPS turns off the faucets in camping areas across the park so the pipes can dry out before a freeze. Visitor centers and comfort stations run on municipal water and are a separate system. The Great Falls Tavern restrooms appear on the NPS list as potable, and so does the Swains Lockhouse. The Swains hiker-biker faucet is already off.
Billy Goat Trail Section A has its own closure rule, set by the river. NPS closes it when the Little Falls gauge reaches 5 feet and reopens it when the reading falls to 4.8 feet, though it may close at lower levels in some conditions. The Great Falls Tavern Visitor Center takes calls about trail status at 301-739-4200 during business hours.
The Visitor Center Cuts Back on December 1
The tavern's hours shrink in two steps. In November, the Great Falls Tavern Visitor Center is open 9 a.m. to 4 p.m. Wednesday through Saturday and Sunday, and closed Monday and Tuesday. From December 1 through February 28, it adds Wednesday to its closed days and opens only Thursday through Sunday, 9 to 4.
Here are the dates that matter between now and the end of the year:
- Around the end of October: the C&O Canal Trust's estimate for restored parking at Swains Lock. NPS describes the closure as lasting several weeks from October 13.
- Mid-November: faucets in park camping areas are typically shut off for the season.
- Thursday, November 26: Great Falls Tavern Visitor Center closed for Thanksgiving.
- Tuesday, December 1: winter hours start at the visitor center, Thursday through Sunday only.
- Sunday, December 13: the C&O Canal Association's continuing hike, 11 a.m. to 3 p.m.
- December: DC Water's projected completion of the Pennyfield repairs, with site restoration in January.
- Thursday, December 24 and Friday, December 25: visitor center closed both days.
The December 13 outing starts at Great Falls too. The C&O Canal Association's listing describes a hike of about five miles, from the Great Falls Overlook Trail down to the crossover at Old Angler's Inn and back along the canal. The park's Holidays at the Tavern weekend is the other December event at Great Falls. NPS hasn't posted its 2026 schedule yet.
A Night at the Lockhouses Costs Less in the Off-Season
Off-season rates are lower at both of Potomac's overnight lockhouses. The C&O Canal Trust's Canal Quarters program rents Lockhouse 21 at 10700 Swains Lock Road for $135 a night from November through April, down from $175 May through October. An $80 cleaning and maintenance fee applies to the first night. The house is furnished to the 1910s, when the canal was still running. The Swains family owned the property for more than 100 years before donating it to the park in 2005, and the interior tells their story through scrapbooks, photographs and games. Guests bring their own linens.
NPS says Lockhouse 21 stays accessible throughout the parking-lot work. The Trust blocked some dates on its booking calendar during the repairs and emailed guests whose reservations were affected.
Upstream, Lockhouse 22 at Pennyfield goes for $75 a night from November through April. The Trust notes that DC Water's repairs may partly block the Pennyfield lot but don't cut off the lockhouse from the towpath.
That gives Potomac two overnight lockhouses for the winter, each just inside a work zone, and one fully staffed day-use entrance between them at Great Falls.
The Shively Team works across Potomac, from homes off MacArthur Boulevard and Falls Road out to the lanes near Swains Lock and Pennyfield Lock. If you're curious what your Potomac home would bring this winter, request a complimentary home valuation.
