Neponset River Report Card: 2021

On July 15, 2022, the U.S. Environmental Protection Agency (EPA) issued the 2021 Water Quality Report Card for the Neponset River and the bacteria “grades”, which can be seen on the map below.

The report card shows the result of water samples taken from various locations across the 120-square mile Neponset River Watershed and is made possible through NepRWA’s Community Water Monitoring Network (CWMN).

For bacterial pollution in the Neponset Watershed, most streams and river segments earned grades of “A” or “B.” Only Unquity Brook, Germany Brook, and Meadow Brook received grades of “D” or “F.” All monitored ponds earned “A’s” and the mainstem of the River, where most recreation occurs, got “B” grades. (Scroll down to learn what A, B, C, D, and F mean.)

NepRWA also tracks dissolved oxygen and phosphorus, which are important for fish, wildlife, and recreation.

The grades in the Neponset are similar to the previous year. (See 2020 Report Card) The biggest challenge in the Neponset is polluted rain runoff from streets, parking lots, and yards. When it is raining, grades drop by 22% on average, nearly two full letter grades.

If you have any questions about the Water Quality Report Card, please contact NepRWA River Restoration Director, Sean McCanty at

What’s in a grade?

The report card grades are based on Massachusetts standards for swimmable water and a less stringent criteria for boating, defined by all 3 of the Boston Harbor watershed associations.

The grades reflect the number of sampling events that either met boating standards (50% compliance) or both swimming and boating standards (100% compliance) over the last 3 years.

While useful, we caution that compliance scores can only tell you how often the standards are met on average and cannot replace your own good judgment about the safety of recreation.

In general, we recommend avoiding water-based recreation, especially swimming, directly following rainy days, as E. coli levels typically spike then.

The multiple factors that affect water quality and the bacteria “grade” of the Neponset River include:

  • Stormwater runoff occurs during rain events and washes contaminants such as dog waste into streams and ponds via storm drain systems.
  • Leaking sewer pipes or sanitary sewer overflows, which allow raw sewage to flow into streams and ponds.
  • Poorly maintained septic systems, which allow bacteria and chemicals to flow from groundwater into streams and ponds.

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