Potomac Interceptor Information

While fluctuations in water quality can be influenced by various factors in addition to the Potomac Interceptor incident, such as runoff from rainfall, sampling in the Washington metropolitan area has generally shown decreased bacteria levels over time and distance from the incident site. Test results of March 24 samples show bacteria levels would meet recreational contact standards at all eight MDE monitoring locations. The area received significant rainfall March 16 and March 17.

A precautionary shellfish harvesting closure that was implemented for a portion of the Potomac River following the incident was lifted on March 10. Water quality testing has shown no evidence that any shellfish harvesting waters are affected by the Potomac Interceptor incident.

MDE Non-Shellfish Sampling Results

MDE Shellfish Waters Sampling Results

On January 19, 2026, the Potomac Interceptor experienced a breach, releasing an estimated 243–300 million gallons of untreated wastewater from a 72-inch DC Water main into the Potomac River. Remediation efforts have been ongoing for the past 25 days. As a precaution, emergency shellfish closures are in effect from Charles County to the Route 301 Bridge, and health advisories remain active in Montgomery, Prince George’s, and Charles counties. All active Maryland drinking water intakes are upstream and unaffected. The bypass system is operational, helping to manage the overflow, though some secondary discharges may still occur due to pump clogs and snowmelt.

This event is classified as a sanitary sewer overflow (SSO), which happens when untreated wastewater is released from a sewer system due to infrastructure failure, blockages, or pump malfunctions.

Press Releases

Maryland health officials provide update on recreational water advisory for Montgomery County impacted by Potomac Interceptor spill (March 17, 2026).

Maryland Department of the Environment Lifts Precautionary Shellfish Harvesting Closure in Potomac River (March 10, 2026).

Maryland Health Officials Provide Update on Recreational Water Advisories for Counties Impacted by Potomac Interceptor Spill (March 5, 2026).

Maryland Department of the Environment Releases Latest Sampling Results Maintaining Positive Shellfish Conditions After Potomac Interceptor Spill (Feb. 25, 2026).

Maryland Department of the Environment issues update on Potomac Interceptor support and response (Feb. 20, 2026).

Key Agencies

District of Columbia Water and Sewer Authority (DC Water): Pipe owner/operator; responsible for bypass, repairs, cleanup, and public signage. Gives operational updates to state and federal partners
United States Environmental Protection Agency (EPA): Primary regulator and lead federal enforcement and compliance authority; enforces federal Clean Water Act regulations and oversees DC Water/Blue Plains consent decree.
Maryland Department of the Environment (MDE): Regulates unauthorized discharges into Maryland waterways and wetlands, monitors shellfish harvesting, and oversees drinking water safety and enforcement.
Maryland Department of Health: Coordinates with local health departments on water contact advisories.
Virginia DEQ & VDH: Monitors downstream water quality and public health.
DC Department of Energy and Environment: Supports water, quality, monitoring, and issuing public health advisories for District residents.
Supporting Entities: National Park Service and the Interstate Commission on the Potomac River Basin coordinate monitoring, modeling, and river management, as well as oversee some permitting.

Environmental Impacts

Category	Status	Details
Drinking Water	SAFE	Intakes are located upstream of the spill.
Shellfish	CLOSURE LIFTED	Precautionary closure from Charles County to Nice Bridge lifted March 10. No active leases and no closures further downstream.
Recreation	PARTIALLY LIFTED	Health advisory partially lifted in Montgomery County.
Recreation	ADVISORIES LIFTED	Health advisories no longer active in Prince George’s and Charles Counties.
Containment	EMERGENCY REPAIRS COMPLETED	Sewage flow that had been carried via installed bypass returned to Potomac Interceptor.

Maryland Department of the Environment (MDE) Response Actions

Coordination, Directions and Inspections

The response efforts include daily coordination, with consistent site visits. The primary goal of these visits is to oversee containment activities and assess the extent of the environmental damage caused by the incident.

Shellfish Protections

To safeguard public health and ensure consumer safety, a precautionary harvesting closure has been issued, encompassing the area from Charles County up to the Route 301 Bridge. As part of this measure, water samples are being collected and sent for analysis.

Ongoing Monitoring

A coordinated monitoring plan has been implemented to track the situation at the spill site and other locations in Maryland and Washington, D.C. As ice continues to clear, efforts will focus on collecting additional samples from open water areas.

Health Coordination

State and local health departments are receiving support to disseminate essential public safety advisories in the three counties impacted by the incident, ensuring residents are informed and protected.

Long-Term Recovery

Restoration plans for the affected areas will be reviewed and approved in close coordination with key partners, including the U.S. EPA and the National Park Service.

Timeline

January 2026	Agency	Action / Response
Jan 19	DC Water	72-inch Potomac Interceptor sewer line collapsed, DC Water began emergency response, investigating the collapse and reporting the ongoing overflow
Jan 20	MDE	Conducted first site inspection, alongside EPA (lead response agency) and DC Water
Jan 21–23	DC Water	Crews worked to install bypass pumps to reroute wastewater around the damaged section
Jan 24	DC Water	Bypass system completed and activated, diverting most wastewater back into the system and containing some overflow
Jan 24	MDH, PG County Health Dep, Charles County Health Dep	Health advisories issued for citizens to avoid direct contact with the river
Jan 25	MDE	Issued a precautionary shellfish harvesting closure north of the Route 301 Bridge, before impacts were confirmed, to protect public health and market confidence
Jan 25–30	DC Water	Excavation began to access the damaged pipe; trench shields and soil stabilization installed. Testing for E. coli and bacterial contamination began at multiple sites
Jan 29	MDH, Montgomery County Health Dep	Health advisories issued for citizens to avoid direct contact with the river

February 2026	Agency	Action / Response
Feb 5	DC Water	Inspection revealed a significant rock blockage inside the collapsed pipe, complicating repairs, iInitial water quality test results show mostly decreasing trends since the start of sampling
Feb 6	DC Water	Released key findings estimating about 243 million gallons had spilled before containment
Feb 12	MDE	Collected samples at routine shellfish sampling stations for analysis
Feb. 13	MDE	Appeared before Maryland General Assembly subcommittee
Feb 17	MDE	Began regular sampling of non-shellfish waters
Feb 25	MDE	Released sampling results showing no evidence shellfish harvesting waters affected by incident

March 2026	Agency	Action / Response
March 3	MDE	Test results of samples show bacteria levels would meet water quality standards for recreational contact at all MDE monitoring locations
March 5	MDH, PG County Health Dep, Charles County Health Dep	Non-contact health advisories issued advising citizens to avoid direct contact with the river lifted
March 10	MDE	Precautionary shellfish harvesting closure lifted
March 12	MDE	Letter to DC Water requesting proposed schedule for remediation and restoration plan submission
March 14	DC Water	Emergency repairs completed, sewage flow that had been carried via installed bypass returned to Potomac Interceptor
March 17	MDH, Montgomery County Health Dep	Non-contact health advisories issued advising citizens to avoid direct contact with the river partially lifted