December 19, 2023

Avoid Contact with the Charles River in Cambridge Due to Potential Harmful Bacteria and Other Pollutants Until December 21, 2023

Public Warning in effect until December 21, 2023

People and pets should avoid contact with the lower Charles River from December 18-21 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. A SSO is an unintentional discharge of wastewater to the environment prior to reaching a treatment facility. SSOs occur infrequently, when the capacity of the sewer system is exceeded—usually due to extreme conditions such as heavy rainfall or an obstruction or break in sewer lines.

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

A CSO release occurred on December 18, 2023 between Magazine Park and the Boston University Bridge (MWR201 – Cottage Farm). It began at 1:23 p.m. and ended at 4:48 p.m. This warning is in effect until 4:48 p.m., Wednesday, December 20, 2023.  

The impacted areas of the Charles River may include the Cambridge and Boston sides of the river just upstream of the Boston University Bridge to the Mass. Ave. Bridge.

A SSO discharge occurred on December 18 and 19, 2023 from Bradeen Street/North Gate (Boston/Roslindale – Bradeen Street). It began at 6:50 p.m. and ended at 4:10 a.m. This warning is in effect until 4:10 a.m., Thursday, December 21, 2023.  

The impacted areas of the Charles River may include the Cambridge and Boston sides of the river between the Esplanade and Science Museum.

The public should avoid contact with impacted areas of the 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. 

Information about Cambridge CSO events are posted on the Cambridge Department of Public Works website.  Additional information is available on the Massachusetts Water Resources Authority and City of Somerville’s websites. 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:

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 [email protected] or 617-665-3838.

Translated Information

For more information, please visit these websites. Find the “Translate” box at the top corner on the right and select your language.


ለበለጠ መረጃ፣ እባክዎን ድህረ ገጾቹን ይጎብኙ። በቀኝ በኩል በላይኛው ጥግ ላይ ያለውን “Translate” የሚለውን ሳጥን ይፈልጉ እና ቋንቋዎን ይምረጡ

Haitian Kreyòl 

Pou plis enfòmasyon, tanpri vizite sit entènèt sa yo. Jwenn bwat “Translate” nan kwen anwo dwat epi chwazi lang ou.


Para mais informações, visite esses sites. Encontre a caixa “Translate” no canto superior à direita e selecione seu idioma.


Para obtener más información, visite los sitios web. Busque el cuadro “Translate” en la esquina derecha superior y seleccione su idioma.