Sewage Overflow
Local response to sanitary sewage overflow in St. Mary's County
Sewage Overflow Incidents
A Sanitary Sewer Overflow (SSO) is a loss of wastewater or discharge from a sanitary sewer system, resulting in the direct or potential discharge of raw, partially treated, or diluted sewage into the Waters of the State. Public utilities are required to report all SSO’s occurring in St Mary’s County to the St. Mary’s County Health Department (SMCHD) and the Maryland Department of the Environment (MDE).In the event of a SSO in St. Mary’s County, SMCHD will:
- Verify that the cleanup of the SSO has occurred
- Ensure that ‘No Contact’ signs have been posted at the site of the SSO
- Consult with MDE and the Maryland Department of Health (MDH) as needed
- Keep the community informed and updated with the SSO
When a wastewater discharge occurs upstream of St. Mary’s County
- MDE evaluates the magnitude and location of the release.
- Hydrologic modeling and plume predictions may be used in determining the need for downstream shellfish and recreational advisories. River dilution, tidal exchange, and turnover rates are also considered.
- Shellfish monitoring continues unless weather conditions make sampling unsafe.
- SMCHD determines if additional monitoring or advisories are needed during the recreational beach season.
Recreational Water Safety
Swimming, fishing, crabbing, kayaking, and other activities in natural waters are never risk-free – even when no advisories are in place.When Recreating in Natural Waters
- Wash hands with soap and water after contact with river water.
- Shower as soon as possible after water recreation
- Wash or sanitize hands before eating
- Avoid water contact if you have open cuts or wounds (or cover wounds with waterproof bandages)
- Postpone swimming for 48 hours after heavy rainfall
- Properly dispose of diapers and pet waste
- Do not drink natural recreational waters unless appropriately treated and filtered
Winter Conditions and Risk
Bacterial levels in natural waters may be higher in winter due to:
- Colder temperatures slow bacterial die-off
- Reduced ultraviolet (UV) sunlight
- Snowmelt washes accumulated animal waste into waterways
- Frozen ground increases runoff
- Changes in salinity and pH during thaw events
Because of these natural seasonal factors, baseline bacterial levels may be higher during winter months.
Seasonal Beach Monitoring in St. Mary’s County
Regulated Beach Season: Memorial Day – Labor Day
Environmental Health team members conduct routine water quality monitoring at public beaches in St. Mary’s County during the regulated beach season. Samples are collected and submitted to the Maryland Department of Health Central Laboratory.
Estuarine beach samples are analyzed for enterococcus, a bacteria found in the intestinal tract of humans and animals. Elevated levels from human sources may increase the risk of gastrointestinal illness or eye irritation. Lab results are reviewed for compliance with health-based criteria established by the EPA and adopted into Maryland regulation as the Beach Action Value (BAV).
When a Beach Action Value is Exceeded
- A public advisory is issued.
- Beaches are not closed, but water contact should be avoided.
- Follow-up sampling continues until results return below the BAV.
Results are posted on the SMCHD Beach Monitoring webpage below:
Shellfish Monitoring
Shellfish harvesting waters in Maryland are regulated and monitored by the Maryland Department of the Environment (MDE).
Shellfish monitoring
- Tests for fecal coliform bacteria
- Protects public health from contaminated seafood
- Uses standards that are more conservative than recreational water criteria
- May result in shellfish area closures when necessary
Shellfish advisory thresholds are stricter than recreational water advisory thresholds (i.e., shellfish area closure may happen sooner and stay in effect longer than a recreational water advisory).
Shellfish closures are precautionary and may remain in effect longer than recreational advisories due to the bioaccumulation potential in shellfish. For information on shellfish closures click the button below:
Reported Sanitary Sewage Overflows
Information on reported SSOs in Maryland can be found here:
Potomac Interceptor Sewer Overflow
Updated March 17, 2026
The Maryland Department of Health announced that the Montgomery County Department of Health and Human Services has partially lifted its recreational water advisory.
Updated March 11, 2026
An upstream wastewater infrastructure failure in the Washington, DC region resulted in sewage discharge into the Potomac River beginning January 19, 2026. Repairs to the Potomac Interceptor sewer line are ongoing, and intermittent releases have been reported during repair efforts.
The St. Mary’s County Health Department (SMCHD) is working closely with state partners to monitor information related to this incident. Based on hydrologic modeling and plume projections, the Maryland Department of the Environment (MDE) issued a precautionary shellfish harvesting area closure affecting portions of the Potomac River in Montgomery, Prince George’s, and Charles Counties.
Severe winter weather initially prevented safe sampling for several weeks. Once conditions improved, MDE resumed monitoring of shellfish harvesting areas in the Potomac River, including in St. Mary’s County. Multiple groups have been conducting sampling at the overflow site along with the sites located upstream and downstream from the event.
On March 10, 2026, MDE allowed the precautionary shellfish area closure to expire after multiple shellfish area samples collected along the Potomac River corridor remained below the indicator bacteria thresholds required for a shellfish harvesting closure. Precautionary recreational water advisories that had been issued downstream from the event have also been lifted in Prince George’s County and Charles County. The Montgomery County recreational water advisory remains in effect at this time.
In St. Mary’s County, MDE continues to monitor shellfish harvesting waters. All local results to date have remained below the thresholds that would require a shellfish harvesting closure. Shellfish monitoring thresholds are more conservative than recreational water advisory thresholds, meaning shellfish closures may occur sooner and remain in effect longer when contamination is present.
Additional monitoring upstream in Prince George’s County and Charles County has included enterococcus testing. Results from those locations have also remained below advisory thresholds, and additional monitoring locations were added on March 10, 2026 to further track water quality conditions.
What this means for St. Mary’s County Residents
At this time, there are no recreational water or shellfish harvesting advisories in effect for St. Mary’s County related to the Potomac Interceptor sewer overflow.
MDE continues to conduct water monitoring for shellfish areas in the Potomac River, including waters in St. Mary’s County. SMCHD will continue to monitor the situation in coordination with state partners and will provide updates if conditions change.
Individuals who recreate on the Potomac River in St. Mary’s County should continue to follow routine hygiene precautions when contacting natural waters. This includes washing hands before eating, showering after water contact, and avoiding contact with the water if you have open cuts or wounds.
Note that winter environmental conditions can increase bacterial survival and runoff, which may naturally elevate bacteria levels in waterways even in the absence of sewage events.
Learn More
Additional updates are available from the Maryland Department of Health and the Maryland Department of the Environment:
- Maryland Department of Health
- Maryland Department of the Environment
- DC Department of Energy and Environment
- Maryland Department of the Environment
Responding Agencies
Contact Us
For local inquiries, contact:
St. Mary’s County Health Department
Environmental Health Division
Email: smchd.env@maryland.gov
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