Summer 2022 Water Quality Reports (CWMN)

Water quality declined as the drought got worse over the summer.

Due to staffing shortages at the Massachusetts Water Resources Authority (MWRA) labs, much of our water quality data has been delayed this season. However, we’re able to update you on what happened in June and July.

The following data comes from water samples taken from 41 sites in the Neponset River Watershed by our Community Water Monitoring Network (CWMN) volunteers. The data in this report is from two sampling events over the two months and should not be taken as representative of the water quality over the entire summer.

Overall, water quality declined as the drought got worse over the summer. We saw dissolved oxygen decline and E. coli levels climb as water levels dropped and became stagnant. However, phosphorus values seemed to improve in July, possibly as a result of almost no stormwater runoff during the month – with algae and plants using up more of the available phosphorus

For any questions about the June and July CWMN results, please email NepRWA Environmental Fellow, Eleanor Yeomans, at

E. Coli

E. Coli is a type of bacteria 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. Wet weather tends to wash a lot of pet and animal waste into our streams.

Wet weather in June was reflected in our E. Coli data, with only 11/41 sites (27%) remaining safe for swimming.  Recreation was still possible, with only 8 sites found to be unsafe for boating. These data show how wet weather conditions can increase E. Coli levels from stormwater runoff. Stormwater Best Management Practices (“BMPs”) like rain gardens and infiltration trenches would help mitigate this impact to clean the stormwater before it discharges to the river. Learn more about BMPs

In July, the worsening drought made our E. coli data worse, with only 7/41 (17%) sites safe for swimming, in dry weather! 15 sites were also unsafe for boating, making recreation hard, especially when people want to get out of the heat! This demonstrates the intensity of drought on our water, with low flows leading to stagnant water and bacteria taking the opportunity to multiply.

June E. Coli Results

July E. Coli Results


Phosphorus is a key nutrient for proper plant growth. Fertilizers, when used incorrectly, can contain high levels of phosphorus and when it is washed off lawns via rain, the it can end up in streams and ponds. Phosphorus fertilizers are regulated within the Neponset River Watershed to help lessen these types of phosphorus loading. Other sources include organic material, pet and animal waste, and even car exhaust. Too much phosphorus can lead to harmful algal blooms, cyanobacteria blooms, and fish kills as oxygen levels drop.

Total phosphorus levels were relatively mild in June, with 75% of the sites tested having healthy phosphorus levels. Phosphorus levels typically increase over the summer, as the weather gets warmer. This increase is largely the result of high water temperatures and low dissolved oxygen, leading to a chemical reaction that releases phosphorus from lake sediments. Another factor is phosphorus-rich organic material such as leaves and pollen washing off paved surfaces and into storm drains.

In July however, we saw phosphorus levels go down, though the same number of sites failed to meet their phosphorus standards. While we typically see an increase, the prolonged drought may be limiting the addition of more phosphorus from the streets into the waterways, and algae and other plants are using up what’s available.

You can help reduce phosphorus pollution by supporting investments in green stormwater infrastructure and stormwater utilities in your neighborhood and reducing your use of synthetic fertilizers.

June Total Phosphorus Results

July Total Phosphorus Results

Dissolved Oxygen

Dissolved oxygen is important for aquatic life because many underwater organisms need oxygen, just like we do. They get it from the water like we get it from the air. Certain animals, including trout, require more dissolved oxygen than others. Low dissolved oxygen levels are linked to drought conditions and sustained high temperatures and can lead to a reduction in the population sizes of the numerous aquatic species that are reliant on oxygen in the water.

June had medium levels of dissolved oxygen, with 85% of sites having enough oxygen to support warm water life, including all of our cold water streams (with only 1 below the cold water standard) indicate that the waterways in the Neponset River Watershed offer a healthy habitat for plants and animals!

However, in July the dissolved oxygen levels got worse, with 26% of our sites falling below the warm water standard. July data is also currently incomplete, so the final result could actually look worse. Alarmingly, one of our cold water sites also fell below the minimum standard, Mill Brook in Westwood, which could jeopardize the coldwater fish in the stream. 3 other cold water sites fell below the higher standard, which suggests the drought is endangering our most threatened populations.

All of this is undoubtedly the result of the drought – high temperatures, lower water levels, excessive algae growth, and less water mixing results in oxygen levels dropping. This can result in fish kills and other loss of aquatic life. We hope for rain in the near future to help our aquatic friends!

June Dissolved Oxygen Levels

July Dissolved Oxygen Levels



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.