August/September 2020 Water Quality Report – CWMN

Dry weather means dry streams and low Dissolved Oxygen 

Long-time CWMN volunteer, Jim Cianci, tests the pH of water samples during COVID-19.


Once a month, 50 alarm clocks ring at 5:30 AM across the Neponset Watershed as our team of volunteers pack their coolers, put on their safety vests, and venture out into the early morning.

In August, volunteers were greeted by the calm of a summer morning. In September, they glimpsed the beginnings of fall foliage along the streams.

These hardy volunteers have the privilege of knowing the Neponset and watching it change through the seasons, droughts, and rainstorms. They are NepRWA’s eyes and ears and provide us with the data we need to keep the river healthy. We are very grateful for their time and effort.

E. coli Results

E. coli is a bacteria that often indicates contamination from human and animal waste.  The bacteria associated with this waste can make people sick. 

In both August and September, 51% of sample sites met the EPA swimming standard. 83% met the boating standard in August while 75% met the boating standard in September. These results are fairly consistent with the E. coli levels in June and July. High E. coli levels continue to impact Unquity Brook, Pine Tree Brook, Pequit Brook, and Hawes Brook.  

Residents can help reduce the amount of E.coli bacteria in the water by always picking up after your dog and throwing the waste in a trash can — and by making sure that your septic system is working properly. The E. coli results are summarized in the map below. 


Dissolved Oxygen Results 

Dissolved oxygen has been referred to as the “air” fish breath underwater. If the concentrations of oxygen in the water get too low, fish and other aquatic organisms can not survive. Low dissolved oxygen is often the result of too much decomposition of algae caused by excess nutrients in the water body.  

Dissolved oxygen levels were very low in August, with only 50% of sites having healthy oxygen levels. This is significantly worse than the results in June (80%) and July (83%). As a result, the amount of high-quality habitat available to fish and aquatic insects during August was very limited.

These low dissolved oxygen levels are linked to drought conditions and sustained high temperatures. As temperatures cooled in September, dissolved oxygen levels increased with 80% of sites reaching healthy levels. The maps below illustrate the results. 


 Phosphorus Results 

Phosphorus is a key nutrient for plants and is a large component of most fertilizers. Unfortunately, when fertilizer washes off lawns it can end up in streams and ponds. Too much phosphorus can lead to harmful algal blooms, cyanobacteria blooms, and fish kills. In August, 76% of sampling locations had unhealthy levels of phosphorus; which is a significant drop when compared to 98% in July. Phosphorus levels continued to fall into September when only 53% of sites were at unhealthy levels. The graph below illustrates the results.

For tips on how to reduce your phosphorus impact on the river visit


Thank you to all of the dedicated volunteers who make up the backbone of the CWMN program! If you have any questions about the CWMN results, please contact Declan Devine at 


Leave a Reply

Your email address will not be published. Required fields are marked *

This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.