Avoid Contact with Alewife Brook Through May 23 Due to Potential Harmful Bacteria and Other Pollutants

People and pets should avoid contact with Alewife Brook and parts of the Mystic River from May 21-23, 2023 due to the release of stormwater mixed with sewage into the river.

The release of mixed stormwater and sewage—known as a “combined sewer overflow (CSO)”—is needed to prevent contaminated water from backing up into homes, businesses, and city streets.

State regulations require local public health departments to notify the public when these discharges may create a risk to public health, including when a discharge lasts for more than 2 hours.

Two CSO releases occurred in Cambridge early Sunday morning, May 21 that lasted more than 2 hours:

A release occurred in Alewife Brook Reservation in North Cambridge (CAM401A), which began at 11:20 p.m. and ended at 1:47 a.m., lasting 2 hours and 27 minutes.

A release occurred in Alewife Brook Reservation in North Cambridge (CAM001), which began at 11:50 p.m. and ended at 1:58 a.m., lasting 2 hours and 8 minutes.

Impacted areas may include the Alewife Brook and Little River in Cambridge, Somerville, and Arlington, as well as the Mystic River from the intersection of Alewife Brook Parkway and Mystic Valley Parkway in Somerville to the Fellsway/Route 28 bridge in Medford (near the Mystic River State Reservation).

The public should avoid contact with impacted areas of the Alewife Brook and Mystic River for 48 hours from the time the overflow ends because of increased health risks due to bacteria or other pollutants carried by the stormwater, such as fertilizers or pesticides. Contact with this water can make you and your pets sick. Avoid paddle boarding, boating, fishing, or other activities that can bring you in close contact with this water.

For more information, go to the Cambridge Department of Public Works’ CSO events web page (www.cambridgema.gov/CSOReport). Additional information is available on the Massachusetts Water Resources Authority (https://bit.ly/MWRA-CSO-Notifications) and the City of Somerville websites (https://www.somervillema.gov/cso). Translations of the web pages are available using the translate box along the top of the websites.

The City of Cambridge continues to make major improvements to the city’s sewer and stormwater systems. As a result, there are fewer CSO events than in the past, but they still occur after heavy rain. To learn more, please visit: www.cambridgema.gov/csoPlanning.

The state law requiring public notification of sewage discharges into waterways took effect in 2022. Environmental groups advocated for the law because they were concerned that Massachusetts had no system in place to alert residents when sewage discharges occurred and what people could do to avoid illness. The new law requires municipalities to alert residents in multiple ways when discharges occur and to make the information available in other languages.

If you have questions about potential health risks from contaminated water, contact Sam Lipson at the Cambridge Public Health Department at slipson@cambridgepublichealth.org or 617-665-3838.