September 2021 Water Quality Report (CWMN)

An extra big thank you to our CWMN volunteers who quite literally weathered the storm for our September water sampling event.

Ponkapoag Brook in Canton after 1″ of rain.

September’s sampling event involved over 50 volunteers at 41 sites throughout the Watershed. Some volunteers visited a single site, while others visited upwards of five sites, taking water samples and dissolved oxygen measurements along the way. Water samples are analyzed at Deer Island for bacteria and nutrients, and all of the data is used by the Massachusetts Department of Environmental Protection (DEP) to uphold the Clean Water Act.

E. coli

E. coli is a bacterium that lives in the intestines of healthy animals, including humans. Its presence in water is evidence of waste contamination. Typical sources of E. coli include leaking sewer infrastructure and bird or dog feces. High levels of the bacteria associated with this waste can make people sick.

This September, we experienced high rainfall with a total of 6.64 inches for the month. This is over 1.5x the average rainfall in September from 1891-2020. (Thanks to the Blue Hills Weather Observatory for providing the long-term data!) These high levels of rainfall led to higher amounts of pollution entering the river via storm drain runoff and the accompanying high E. Coli levels that we observed. In 2019 and 2020, roughly 25% of CWMN sites were not safe for recreation in September. In 2021, we saw that increase to over 35% of sites.

This data shows the importance of structural stormwater Best Management Practices (“BMPs”), which help to treat stormwater and clean it before it discharges to the river. You can find more information about BMPs on the Neponset River Watershed Association website.

The E. coli results are summarized in the maps and graph below. Note that there was no E. coli data collected for MMB106.


Total Phosphorus

Phosphorus is a key nutrient for proper plant growth. For this reason, fertilizers contain phosphorus and when it is washed off lawns via rain, phosphorous can end up in streams and ponds. Too much phosphorus can lead to harmful algal blooms, cyanobacteria blooms, and fish kills.

Total phosphorus levels were high in September. Only 2 of the river sampling sites met the lower (.1 mg/L) total phosphorus standard and none of our pond sites met their standard (.025 mg/L). Just as high rainfall contributed to increased E. coli levels, an unseasonably wet September was likely the culprit for our high total phosphorus levels. Increased rainfall means more runoff carrying nutrients from lawns and other maintained pieces of land such as agricultural fields and golf courses.

You can help reduce phosphorus pollution by supporting investments in green stormwater infrastructure and stormwater utilities in your neighborhood.

The phosphorus results are summarized in the graph below. Note that there was no phosphorus data collected for EAB010 and MMB106.

Dissolved Oxygen

September’s dissolved oxygen measurements bring some good news for the aquatic life that resides in the Neponset River Watershed! Dissolved oxygen is important for our aquatic life because dissolved oxygen is how many of these underwater critters access the oxygen they need to respire or breath. Certain animals, including trout, require more dissolved oxygen than others. Low dissolved oxygen levels are linked to drought conditions and sustained high temperatures, which weren’t of particular concern this September.

Nearly 80% of our sites with dissolved oxygen measurements taken reached the recommended number of milligrams of oxygen per liter for warm water fish and over 70% reached the recommended number of milligrams of oxygen per liter for cold water fish.

The dissolved oxygen results are summarized in the graph below. Note that there were no dissolved oxygen measurements collected at HAB006 and WIP003.


All of this data has gone through preliminary quality control, however, note that a more extensive overview is given to the data before reporting it to DEP.

For comments, questions — or to learn more about becoming a CWMN volunteer — please contact NepRWA’s Environmental Science Fellow, Eleanor Yeomans at or 781-575-0354 x 302.


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