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How do you ensure there's always enough water to serve almost two million customers? WSSC Water's answer: dams and reservoirs.

WSSC Water owns and maintains three dams that provide drinking water to our 1.9 million customers in Montgomery and Prince George's counties: the Brighton Dam, the T. Howard Duckett Dam and the Little Seneca Dam. The Brighton and T. Howard Duckett dams span the Patuxent River and three counties to create two reservoirs: the Triadelphia Reservoir and the T. Howard Duckett reservoir.

The Triadelphia reservoir is fed by two major tributaries: the Upper Patuxent and Cattail Creek. The T. Howard Ducket Reservoir is fed by water released from the Brighton Dam and by the Hawlings River. The two reservoirs are surrounded by 6,000 acres of wooded property that comprise the WSSC Water-owned portion of the Patuxent Watershed. Together, the reservoirs store almost 11 billion gallons of water and create a body of water with a combined surface area of 1,600 acres. The reservoirs supply water that is treated at our Patuxent Water Filtration Plant, which provides drinking water to a portion of customers in Prince George’s and Montgomery counties.

WSSC Water staff inspect our dams every month, and Brighton Dam is inspected annually by the Federal Energy Regulatory Commission and the Maryland Department of the Environment. The T. Howard Duckett and Little Seneca Dams are also inspected annually by MDE.

Drinking Water Protection

WSSC Water dams were built to protect the drinking water supply. When there is heavy or long-lasting rainfall, we release water from the dam to protect the integrity of the structure - a standard and proactive measure.

Since the dams were put into service, WSSC Water has lowered the stored water level by one billion gallons to offer a buffer to increase warning time during flooding conditions. The dams and reservoirs have always reduced peak flooding levels downstream. Both dams maintain a minimum flow-by to the Patuxent River, even during droughts. Since the dams have been in operation, the worst flooding event occurred in June 1972, in the aftermath of Hurricane Agnes.

Brighton Dam and Triadelphia Reservoir
2 Brighton Dam Road, Brookeville, Maryland 20833

The Brighton Dam went into service in 1944. Located on Brighton Dam Road in Brookeville, it spans the Patuxent River between Montgomery and Howard counties, creating the Triadelphia Reservoir. The Brighton Dam has 13 tainter gates. Its reservoir capacity is approximately 6.3 billion gallons, which are released into the Patuxent River, captured by the T. Howard Duckett Reservoir and then sent to the Patuxent Water Filtration Plant for treatment.

T. Howard Duckett Dam and T. Howard Duckett Reservoir
7400 Brooklyn Bridge Road, Laurel, Maryland 20707

The T. Howard Duckett Dam went into service in 1954. Spanning the Patuxent River between Prince George’s and Howard counties, the dam creates the T. Howard Duckett Reservoir. It is 13 miles downstream of the Brighton Dam and has seven tainter gates. Located just off I-95 north of the Capital Beltway, the dam is clearly visible to travelers. The reservoir holds about 5.7 billion gallons of water that travels by an underground pipe to WSSC Water’s Patuxent Water Filtration Plant for treatment.

Little Seneca Dam
Black Hill Regional Park

Located in Black Hill Regional Park, which is operated by the Maryland National Capital Park and Planning Commission, Little Seneca Dam and Little Seneca Lake hold four billion gallons of water. This reservoir is part of the Washington Metropolitan Regional Water Supply. Water is released into Seneca Creek, which travels to the Potomac River to provide water at the region’s three water intakes operated by WSSC Water, Fairfax Water and the Army Corps of Engineers.

Learn more about Water Filtration

Last Modified: December 20, 2021, 10:29 am EST