NepRWA’s water quality reports enable us to advocate for the cleanup of pollution.

Our water sampling begins with the Community Water Monitoring Network (CWMN), an Environmental Protection Agency-approved, volunteer-based approach to water quality monitoring that has been running at NepRWA since 1995.

CWMN volunteers sample water quality in streams and the Neponset River, from May through October, throughout the 14 communities of the Neponset Watershed. The samples provide critical scientific data that assists us in locating and cleaning up pollution around the Watershed.

NepRWA staff produces an Annual Water Quality Report for the Neponset River, as well as individual reports for select towns in the Watershed.

The U.S. Environmental Protection Agency (EPA) has been issuing water quality report cards for the Neponset River since 2019, based on the data from CWMN.

For more information about the CWMN Program and water quality results, please contact NepRWA River Restoration Director, Sean McCanty at

Click below for detailed reports.

2023 Water Quality Presentation

2022 Water Quality Presentation

2021 Water Quality Presentation

2020 Water Quality Presentation

Several Neponset Stormwater Partnership (NSP) communities conduct regular water testing with the help of volunteers in one or more of their watersheds. In other areas, water quality data may be collected by nonprofit groups or the state Department of Environmental Protection from time to time.

The data is used to assess the health of the Neponset River and tributaries for wildlife and recreation, and to locate pollution sources for follow-up sampling.

Learn more about the Neponset Stormwater Partnership (NSP)

The U.S. Environmental Protection Agency (EPA) water quality report cards for the Neponset River show the results of water sampling data made possible through NepRWA’s Community Water Monitoring Network (CWMN). The report cards have been issued to the Neponset River since 2019.

E. coli

The concentration of E. coli bacteria is used to assess a waterbody’s safety for “contact recreation” through activities such as swimming, fishing, boating, and wading.  The presence of E. coli is evidence of fecal contamination and is an indicator of the likely presence of other, more dangerous, pathogens associated with human and animal waste.

The most common sources of E. coli include improper disposal of pet waste in streets, lawns, and catch basins.  Additional common sources include sewer or septic system malfunctions and discharges of organic wastes from household or commercial garbage.

Wildlife waste also contains E. coli, however, elevated concentrations from wildlife are typically associated with human activities, such as feeding ducks.

Management interventions to reduce E. coli loads can include:

  • education on pet waste disposal
  • proper management of solid waste
  • frequent cleaning of catch basins
  • filtration stormwater best management practices (BMPs) to reduce the runoff that reaches a water body
  • rapid identification and repair of sewage leaks and spills.


Phosphorus is a required plant nutrient that is often the “limiting nutrient” in freshwater ecosystems.  Therefore, the concentration of available phosphorus in a freshwater water body will often control the rate of aquatic plant growth (the other required nutrients are typically present at proportionately higher levels).

Excess phosphorus creates excess biomass, especially algae, in a process called eutrophication.  When the excess plants and algae die, the process of decomposition consumes dissolved oxygen, and in extreme cases dissolved oxygen levels get too low to support aquatic animals such as fish.

Other impacts of eutrophication include unattractive and smelly algal blooms and the destruction of underwater plant communities through reduced light penetration.  Elevated phosphorus concentrations can cause harmful algal blooms (HABs), such as cyanobacteria that produce toxins harmful to people.

Phosphorus sources can include wet (from rain) or dry (from sprinklers) weather runoff from parking lots, streets/gutters, and lawns.  These surfaces contain phosphorus from fertilizers, organic matter (leaves, grass clippings), soil, garbage, and pet waste.

Interestingly, phosphorus can also accumulate on these surfaces from atmospheric deposition. Illegal dumping of organic matter such as leaves in or near waterways or catch basins is a common problem.  Poorly maintained septic systems, illicit discharges of sewage, and naturally occurring dead aquatic plant materials are additional sources.


The pH of a waterbody is a measure of how much free hydrogen ion (H+) is present in the water—a lot of free hydrogen ion leads to acidity (low pH) and low amounts of free hydrogen ion lead to more basic conditions (high pH).

Water that is too acidic or too basic can be toxic to aquatic life. The pH is influenced by bedrock characteristics, groundwater seepage, acid rain, or heavy loading of tannin-rich leaves/needles.

Dissolved Oxygen

Adequate concentrations of dissolved oxygen (DO) are necessary to support fish, amphibians, mollusks, aquatic insects, and other invertebrate species.  Many environmental drivers impact the DO levels in a water body.

For example, cooler water temperatures sustain higher levels of DO, which is why there is often a seasonal trend in DO concentration: low levels in the warm months and higher levels in the colder months.  Rapid mixing and turbulence (such as riffles or step pools) also result in high levels of DO due to atmospheric mixing.

Alternatively, large amounts of decaying organic matter consume dissolved oxygen as microorganisms degrade the organic matter, and lower levels of DO result.  Excessive phosphorous that causes eutrophic conditions is also closely associated with low dissolved oxygen levels because it drives plant growth and subsequent decomposition.

In thermally stratified lakes, oxygen-deficient conditions can occur in the deeper portions of the water where there is no atmospheric mixing and no photosynthesis (the two sources of DO in aquatic systems).

In the summer, ponds, and lakes typically have warmer surface waters and thus lower surface DO concentrations.  Management interventions that can increase DO levels include increasing riparian shading to maintain lower water temperatures, removing obsolete dams, reducing excessive water diversions, and reducing decaying organic matter through the reduction of phosphorous runoff and other drivers of eutrophication.

How do I know if the water in my town is clean for swimming, boating, or fishing?

For the most up-to-date information on water quality in your town, check with your local board of health or town website.

While NepRWA monitors water quality in local streams and ponds, the collected data primarily captures trends over time rather than daily fluctuations.