Rock Creek originates from a spring near Laytonsville in Montgomery County, MD and flows south approximately 33 miles before joining the Potomac River near Georgetown in Washington, DC. Within the District, Rock Creek travels 9 miles through Rock Creek Park. The creek is fed by 30 small tributaries and numerous storm sewers, and groundwater.

The watershed of Rock Creek totals 76.5 square miles, and encompasses two sub-watersheds – upper Rock Creek and lower Rock Creek. Public and private property in Montgomery County make up more than 60 square miles of the entire watershed. A highly developed watershed, more than 500,000 people reside within its boundaries. The watershed undergoes changes in land use as you move south through upper Montgomery County into lower Montgomery County and into Washington, DC.