River Restoration and Dams

The many old dams on the Sudbury, Assabet, and Concord Rivers date from the days of water-powered mills, and only two generate electricity today. They serve no purpose for flood control. The mill dams turn sections of the rivers into a series of pond-like impoundments that warm and slow the flow of nutrient-rich water, fueling aquatic weed growth and trapping soft sediments (as much as 10 feet deep) behind each dam.

Aquatic weeds, particularly filamentous green algae and invasive water chestnut, block sunlight and decrease the oxygen in the water necessary for aquatic life. They also out-compete native aquatic vegetation and make river recreation impossible. As the plants die back and sink to the bottom in the fall, the nutrients they took up settle back into the sediments, ready to feed another year’s growth. This phosphorus recycling is a major source of water pollution.

Dams also block the movement of fish and other river wildlife. Fish and other aquatic organisms need to be able to move up and down streams to find food, refuge from drought and heat, and places to breed. These rivers were once home to multitudes of migratory fish that must swim from the ocean into fresh water to breed or mature. They are important species to both the Gulf of Maine fisheries and local river ecology: river herring (blueback herring and alewife), American shad, American eel, and sea lamprey.

To learn more:
Division of Ecological Restoration
American Rivers (Free Rivers: The State of Dam Removal in the U.S., 2022)


The Concord River is impounded in North Billerica by the Faulkner (Talbot Mills) dam, where the river intersects with the Middlesex Canal and further downstream by Centennial Island and Middlesex dams in Lowell. The Middlesex dam is breached, and there is a small hydroelectric facility at the Centennial Island dam, which also has a fishway. Lowell Parks and Conservation Trust conducts herring monitoring at this fishway.

OARS is the Lead Project Sponsor and Project Manger for the Talbot Mills Dam Removal in North Billerica, a Priority Project of the State’s Division of Ecological Restoration. The dam owner wishes to remove it and restore the fish migration between the SuAsCo basin and the Gulf of Maine. This project would restore the largest amount of migratory fish breeding habitat of any dam removal project in the state. This project started in 2021 and will span several years. OARS is committed to the public having access to information about this project so that they can understand it and make input.

Go to the project website to sign up for updates and read the Frequently Asked Questions (English, Spanish, Portuguese, and Khmer)

Follow the fascinating Story Map of the dam site and the Merrimack River history and restoration work

Examples of other dam removal projects:
Local Matters video, Plymouth, MA (starts at 13 min 23 sec)

Announcements and Presentations:
Talbot Mills Public Meeting, June 29, 2022 (Meeting flyer with Zoom link)
Presentation to the Middlesex Canal Association Annual Meeting, May 15, 2022
Talbot Dam Public Meeting , June 29, 2022

Permits and Certificates:
MEPA Secretary's Certificate on Single Environmental Impact Report (SEIR), April. 1, 2024. MEPA Secretary's Certificate on Expanded Environmental Notification Form (EENF), Sept. 1, 202. To see all Comment Letters go to MEPA Environmental Monitor, select the Sept. 25, 2023, edition and then the Secretary's Certificates tab and scroll down to no. 16731 Talbot Mills Dam Removal project in Billerica.

Feasibility study for restoring fish passage at the Concord River dams (2016)
Talbot Mills Dam Removal Targeted Impact Analysis-Draft Report (Jan. 2022)
Review of Talbot Mills Dam Removal Targeted Impact Analysis (prepared for Town of Billerica, April 2022)
Talbot Mills Impoundment Dissolved Oxygen Study 2022

For all the public project documents, click here. For Sec. 106 Historical Review documents click on Section 106 Historical Review folder. For MEPA Single Environmental Impact Report documents click on Permitting Folder, then MEPA folder, then SEIR folder.


There are six old mill dams on the Assabet River. A series of flood-control dams on the Assabet River and its streams were built in 1962-87, which only impound floodwaters. OARS held two workshops on "Assabet River Restoration: Understanding the Impacts of Dams in Your Community" in Westborough and Maynard in March 2009. The workshops moved the discussion forward collaboratively among the 100 participants, building a sound understanding of the science and policy behind these issues.

Assabet River Sediment and Dam Removal Study (2010)

Assabet River Restoration and Dams

NORTH BROOK (Wheeler Pond dam, Berlin, MA):

Learn More about our Wheeler Pond Dam Removal Project

OARS is the Project Manager for the Wheeler Pond Dam Removal in Berlin on North Brook, a tributary to the Assabet River. The dam owner wishes to remove this significant hazard dam in unsafe condition. Its removal will reconnect fragmented wild eastern brook trout habitat, reduce stream temperatures, and reduce the flood hazard. This project started in 2023 and will span several years. OARS is committed to the public having access to information about this project so that they can understand it and make input.

NASHOBA BROOK (Warner's Pond dam, Concord, MA):

Learn More about Warner's Pond Dam

OARS supports the dam removal alternative and seeks to provide accurate scientific information to the public about the impact of removing this dam.

Other information:
OARS work to restore stream continuity


The Saxonville dam in Framingham powered the milltown of Saxonville in the past, while several upstream dams were built in Ashland, Framingham, and Southborough to create water supply reservoirs for the city of Boston. In addition, there are many millponds on tributaries to the three rivers, such as the dams upstream and downstream of the Wayside Inn on Hop Brook in Sudbury.