The Occoquan Basin: Nearly 40% of Prince William County lands drain directly into
the Occoquan Reservoir before flowing to
the Potomac River and on to the Chesapeake Bay.
The Occoquan watershed (drainage area) covers 590 square miles and includes the 1,700-acre Occoquan Reservoir, which serves as the boundary between Fairfax and Prince William counties.
The Occoquan Reservoir supplies about 40% of the drinking water supply for 1.2 million Northern Virginia residents and can supply drinking water for the entire region in an emergency.