Water Quality


The Sudbury, Assabet and Concord Rivers all have a Class B, “fishable and swimmable” water quality classification, although none of the rivers meet this classification at present. The rivers are overloaded with nutrients, particularly phosphorus, which encourage plant growth in the warm summer months, leading to green blankets of algae and duck weed on the surface. This detracts from the beauty and recreational activities on the river, but more importantly it depletes the amount of oxygen in the water which is needed by fish and other aquatic organisms to live. Later in the summer and fall when the plants begin to decay, they create a bad odor.

Nutrients enter the rivers from point sources such as wastewater treatment plants, and nonpoint sources which are carried over land and into the water by stormwater runoff. On the Assabet River, there are four municipal wastewater treatment plants upstream of the designated Wild and Scenic segment which are a main source of nutrients entering the river. These are in Westborough, Marlborough (Westerly), Hudson and Maynard. The town of Concord’s wastewater treatment plant discharges to the Wild and Scenic segment of the Concord River. Municipal discharges to the Sudbury River Wild and Scenic segment include a small plant owned by the town of Wayland and the Marlborough Easterly wastewater treatment plant which discharges to Hop Brook, a tributary of the Sudbury River.  Nonpoint sources of pollution, especially from stormwater and sediments, are a significant portion of the nutrient load as well to all three rivers. Because these rivers are generally slow moving, nutrients have also accumulated in the sediments and are available for plant growth in the summer.

The River Stewardship Council (RSC) is working with many local, state and federal partners to improve water quality on these rivers. Funds have helped to support OARS' water quality program on the Assabet, Sudbury and Concord Rivers. Under Section 7 of the Wild and Scenic Rivers Act, the RSC and National Park Service have spoken out on draft wastewater treatment plant permits to ensure that phosphorus limits are based on science and will enable the rivers to meet their water quality standards. The RSC partners with local groups to educate local citizens about what they can do to help protect the water quality.

What can you do to help?

There are many things that each of us, as an individual, can do to decrease water pollution in the Sudbury, Assabet and Concord Rivers. Each of these actions will help to decrease the amount of nutrients, phosphorus and nitrogen, from reaching the rivers: 

  1. Use phosphate-free dishwashing detergent.

  2. Use phosphorus-free lawn fertilizer, minimize use of all lawn fertilizers, and reduce stormwater runoff. Learn more.  

  3. Practice ecological landscaping

  4. Properly dispose of pet waste


Sediments in the Sudbury River are contaminated with mercury emanating from the Nyanza chemical waste site in Ashland, MA. The full length of the Sudbury's Wild and Scenic segment, to Egg Rock in Concord, is considered to be part of this site and contains high levels of mercury in the sediment. The Environmental Protection Agency oversees the studies of the Superfund site and its remediation. Fish caught in the Sudbury River from Ashland to Concord should not be eaten due to the mercury contamination. A multilingual public information campaign, Fishing4health, provides further information.

The settlement from Nyanza Chemical Company established a Natural Resources Damages Fund. State and federal trustees of the fund are developing a plan to restore the natural resources damaged by the Nyanza Chemical Waste Dump Site, particularly the Sudbury River. To compensate for natural resources and natural resource services injured as a result of mercury contamination, the Trustees seek to restore wetland, floodplain, and riverine habitats and species that utilize or historically utilized these habitats, particularly birds and riverine fish, as well as other aquatic organisms, amphibians, reptiles, and mammals. Learn more about the Natural Resources Restoration Plan.

The Concord, Assabet, & Sudbury Wild & Scenic River Stewardship Council • 15 State Street • Boston, MA 02109

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