The Magothy's tidal estuary portion extends for eight miles from its mouth at the Chesapeake Bay south of Gibson Island.

The source of its four-mile non-tidal portion is a small pond on Woodland Estates Way in Chartwell, just west of Elvaton Park, four miles north of Millersville.

Charles L. Pumphrey and Bill Labrot testified before a Senate Committee in the summer of 1945 against such a use as they, Navy men in World War I, felt that this installation would be detrimental to the beauty and tranquility of the Bay area.

William Labrot gave the land in question to the state on condition that it be a dedicated park, and with the participation of local residents, Charles L. Pumphrey formed and was the first President of the Magothy River Assoc.

Today this organization concentrates on issues concerning land use, water quality monitoring, fish habitat and reforestation programs.

Volunteer scientific divers were organized in 1998 and assist with the restoration and management of underwater grasses and oyster habitats.

[6] The river's overall health score was determined by three contributing factors: underwater grasses, water clarity, and dissolved oxygen.