Lower Assabet River
The Assabet River begins at the outlet of the Assabet Reservoir (Mill Pond) in Westborough and flows northeast to its confluence with the Sudbury River in Concord at Egg Rock. The Lower Assabet segment runs from just upstream of Elizabeth Brook in Stow to the confluence in Concord. It runs through the mill towns of Maynard and the former Damondale (now in West Concord) and contains two mill dams. The portion of this segment from just below the former Damonmill dam (now removed) in Concord to the confluence, together with contiguous sections of the Sudbury and Concord Rivers, was federally designated in 1999 as a Wild & Scenic River, reflecting its natural beauty and free-flowing condition.
The Lower Assabet River received an Overall grade of B. At times of low flow during the summer, most of the water that flows in the Lower Assabet comes from the four municipal wastewater treatment plants upstream. Major improvements in wastewater treatment, particularly nutrient removal, at these plants have resulted in reduced phosphorus pollution. The lower phosphorus concentration in the water column has reduced floating biomass but not eliminated it, with the Floating Biomass indicator receiving a grade of C. This segment of the river has extensive trail networks along it, resulting in a Trails indicator grade of A.