The Concord River basin is situated in Worcester and Middlesex Counties of Massachusetts, and includes the Assabet and Sudbury River basins. The Concord River basin includes all or part of 36 cities and towns, including the city of Lowell and the town of Framingham, the most populous town in the State.

Topography is generally low, with altitudes ranging from about 480 ft in the headwaters area of the Sudbury River and about 420 ft in the headwaters area of the Assabet River to about 50 ft above sea level at the confluence of the Concord and Merrimack Rivers. Unless otherwise noted, the description of the water resources of the Concord River basin is based on Hydrologic Investigations Atlases 312 (Pollock and others, 1969) and 662 (Brackley and Hansen, 1985).