Triadelphia Reservoir 800 acre lake is located on the Patuxent River, in Howard County and Montgomery County, Maryland near the town of Brookeville. The reservoir was created in 1943 by the construction of the Brighton Dam on the Patuxent and is home to a stunning 5 acre woodland garden with over 20,000 azaleas that bloom each May. The reservoir is maintained as a drinking water source by the Washington Suburban Sanitary Commission (WSSC).WSSC provides recreational facilities to the public on portions of the Triadelphia property, including hiking, picnicking, fishing and boating. Wildlife: this location has the most sightings of Bald Eagle.