Triadelphia Reservoir and Rocky Gorge Reservoir are owned and operated by the Washington Suburban
Sanitary Commission (WSSC). Triadelphia is oriented slightly northwest to southeast along the Patuxent River which serves as the boundary between Howard County to the east and Montgomery County to the west. The two reservoirs are surrounded by 6,000+ mostly wooded acres.

Triadelphia is the larger of the two reservoirs and attracts a wide variety of birds not consistently seen elsewhere in the county. Access to this reservoir, although limited, is much better for birders than that at Rocky Gorge. Although boating and fishing are allowed, shore access is minimal. Birders may view portions of this reservoir at three public sites in Howard County: Brighton Dam, Big Branch, and Pigtail.

Reservoirs are open from March 15 to November 30. Day use or seasonal permits are required for boating, fishing (along with state fishing licenses), and birding. Rangers are security personnel. They enforce regulations and issue citations for trespassing as well as for fishing and boating violations.