SuAsCo watershed map
The Sudbury-Assabet-Concord Watershed, located in the metro-west area of the state, encompasses a large network of tributaries that ultimately flow into the Merrimack River. The watershed has a total drainage area of approximately 377 square miles.

The Assabet River flows north about 30 miles from its headwaters in Westborough, through the now densely developed urban centers of Northborough, Hudson, and Maynard, to its confluence with the Sudbury River at historic Egg Rock in Concord, where the Concord River begins. The Sudbury River also has its beginnings in Westborough, flowing eastward from the Great Cedar Swamp toward Framingham. It then proceeds north through the Towns of Sudbury, Wayland, and Lincoln, then into the Town of Concord. The SuAsCo encompasses all or part of 36 municipalities and supports a population of 365,000 people.

Twenty-nine free-flowing miles of the three major rivers in the SuAsCo Watershed were designated as Wild and Scenic on April 9, 1999. The rivers were recognized for their outstanding ecological, historical, scenic, and recreational values, as well as their lasting place in American literature. The SuAsCo also encompasses two National Wildlife Refuges (NWRs) - the Great Meadows NWR, located primarily in Sudbury, and the Assabet NWR, located primarily in Stow. The SuAsCo also has the Commonwealth's first designated Area of Critical Environmental Concern - the Great Cedar Swamp located in Westborough. The Great Meadows NWR and the Great Cedar Swamp represent the two of the largest wetlands in Central Massachusetts.

Watershed Priorities

  • Gather sufficient water quality data to help determine the areas most affected by point and nonpoint source pollution
  • Work to understand watershed hydrology to aid in decisions concerning the Inter-Basin Transfer Act and Water Management Act permit requests
  • Work to maintain a healthy and seasonal variability of streamflow to sustain aquatic and terrestrial biodiversity
  • Decrease impervious surface area and local water consumption

Watershed Successes


Fishing at Walden Pond in the SuAsCo watershed
Stream teams were developed on the Concord River in Billerica and Sudbury River in Southborough. These teams help maintain a grassroots presence in the watershed. The results of their surveys will help lay the groundwork for non-point source pollution remediation and future grant targeting.

Alewife spawning occurred in the Concord River for the first time since the early 19th Century. The Middleborough-Lakeville Herring Fisheries Commission provided 7,500 alewives for reintroduction this year and plans to introduce 7,500 more alewives in each of the next two years.

Watershed Publications

Watershed Links

OARS: For the Assabet, Sudbury, and Concord Rivers
Sudbury Conservation Commission
Lowell Parks and Conservation Trust
Sudbury Valley Trustees
Sudbury, Assabet, and Concord Wild & Scenic River Stewardship Council

This information is provided by the Executive Office of Energy and Environmental Affairs, Office of Water Policy