If you have tried to pick up the Muddy Branch Greenway Trail from the River Road end this summer and found a chain-link fence where the trailhead used to be, you have probably asked the obvious question: why is a hiking trail closed for what sounds like plumbing work?

The answer is not a routine parks maintenance note. It traces back to one of the largest sewage spills in U.S. history, and once you see the connection, the closure map on this trail stops looking random. It starts looking like a diagram of exactly where the emergency is, and exactly why the North Potomac side of the trail system has stayed open the whole time.

Where the barricades actually are

Montgomery Parks has been running the same closure notice on its Muddy Branch Greenway Trail page since March: portions of the trail closed through September 2026 for utility repairs to the Potomac Interceptor running adjacent to the path. As of an AllTrails update in July, those same segments were still shut. Here is what that actually covers on the ground.

Every closed segment sits at the river end of the trail, downstream toward Pennyfield Lock. Nothing on the official closure list touches the paved stretch behind Kentlands, the Malcolm King Park loop in Gaithersburg, or the Izaak Walton League access point off Conservation Lane. That is not a coincidence. It is where the actual repair work is happening.

The pipe under the barricades

The Muddy Branch Greenway Trail runs alongside a section of the Potomac Interceptor, the 54-mile sewer line that carries wastewater from parts of Virginia, Maryland, and D.C. to the Blue Plains treatment plant. In January 2026, that line failed. DC Water's Potomac Interceptor ruptured near Clara Barton Parkway and Lock 10 of the C&O Canal in Cabin John, releasing an estimated 240 million gallons of raw sewage into the Potomac River, more than the Tidal Basin can hold. The pollution event was severe enough to contribute to the river's listing among the country's most endangered by American Rivers.

That failure triggered expanded inspections along the rest of the 54-mile interceptor. What those inspections found near Pennyfield Lock, at a point known as Lock 22 where the pipe runs under Muddy Branch, was significant corrosion and exposed rebar in a roughly 1,700-foot section. DC Water classified it as an emergency repair. Crews began staging equipment the week of June 1 and started mobilizing on site June 15, with tree trimming and brush clearing already underway before that. The rehabilitation method is slip lining, threading new pipe inside the damaged section rather than digging it out entirely, and construction is expected to continue through the end of September.

The location matters for anyone trying to understand why the trail is cut where it is. That section of pipe carries an average of six million gallons of wastewater a day on a typical dry-weather day, and it sits upstream of both the WSSC Potomac Water Filtration Plant and the Washington Aqueduct's intakes at Great Falls. The National Park Service, which controls the land the trail crosses at this point, issued a special use permit for the work and has been explicit that all excavation stays within the existing pipeline footprint, with no new ground disturbance and no impact to a historic culvert in Muddy Branch. Parking and visitor access at Pennyfield Lock and Lockhouse 22 itself are staying open even while the trail segments around them close.

None of this is disconnected from what happens next in the neighborhood. In May, Potomac Conservancy leaders attended a congressional oversight hearing on the interceptor collapse, and the EPA and Department of Justice have since sued DC Water over Clean Water Act violations tied to the spill, with Maryland filing its own suit over state water pollution law. The Muddy Branch repair is a direct downstream consequence of that January failure, not an unrelated construction project that happened to land on the same trail.

What's actually still open right now

If your normal loop starts from the North Potomac or Kentlands side rather than River Road, the closures barely touch your usual route. Three access points have stayed off the closure list through the entire construction window:

• The paved segment off Darnestown Road behind Kentlands, which runs under Great Seneca Highway toward an access road looping to Conservation Lane
• The Malcolm King Park loop in Gaithersburg, an easy paved path that the Muddy Branch Alliance describes as a good introduction to the trail for anyone not looking for the rockier sections farther south
• The Izaak Walton League National Conservation Center at 707 Conservation Lane, which has ample parking and connects to the Isaac Walton Trail and Halcyon Lake Loop Trail

The Potomac Horse Center on Quince Orchard Road also remains a working access point, sitting between the neighborhood side and the river-end closures. If your regular route stays north of Darnestown Road, you are unlikely to hit a barricade at all this season.

Reading the September deadline

DC Water's own release states construction is expected to continue through the end of September. Montgomery Parks' language, that portions will be closed through September 2026, lines up with that same window. With today's date at the end of August, that puts the repair roughly one month from its stated completion point, meaning regulars should plan on the river-end closures holding through Labor Day weekend and likely into the final weeks of September before any reopening notice goes up.

Neither DC Water nor Montgomery Parks has published a firm reopening date beyond end of September, and given that this is emergency repair work following a structural failure rather than a scheduled maintenance project, that window could shift. The practical takeaway for anyone planning a fall hike toward Blockhouse Point or Pennyfield Lock is to check the Montgomery Parks trail page before heading out, rather than assuming the barricades from June are still in the same place they were three months ago.

What this closure really tells a North Potomac regular is something most drive-by trail reports miss: the shutdown isn't spread evenly across the trail system because the problem isn't evenly spread either. It sits at one specific point in the pipe, and the closures follow that point almost exactly. Everything closer to the neighborhood, where most daily walkers and bikers actually start their loop, has stayed open the entire time.

If you are weighing what it means to live near a trail system that runs through both a quiet Gaithersburg park and a piece of regional water infrastructure, that is exactly the kind of on-the-ground context Embrey Properties tracks for clients considering North Potomac. Schedule a consultation with our team to talk through what daily life actually looks like in this pocket of Montgomery County, trail access included.