Combined Sewer Overflow Reporting

Cambridge Combined Sewer Overflow (CSO) Reporting

A combined sewer overflow (CSO) occurs when a large storm overwhelms the combined sewerage system causing rainwater to mix with wastewater and discharge to a nearby water body.  This relief measure prevents sewage backups into homes and businesses.  Cambridge owns combined sewer outfalls that discharge to the Charles River and Alewife Brook.  When a CSO occurs at a Cambridge-owned outfall, there will be a notification displayed in the table below.

The Massachusetts Water Resource Authority (MWRA) and the cities of Boston, Chelsea and Somerville manage their own combined sewer outfalls, including CSO reporting.  These communities must be contacted directly for information regarding their CSO discharges. To see where all CSO outfalls are located, download this MWRA map of MWRA and community CSO sites.

Public health officials recommend avoiding contact with water bodies during rainstorms and for 48 hours afterwards, as there may be increased health risks due to bacteria or other pollutants associated with urban stormwater runoff and CSO discharges.  To see what Cambridge is doing to address pollutants from stormwater runoff please visit our stormwater management website and learn how you can also help reduce stormwater pollution.

Subscribe to Cambridge CSO discharge notification alerts.

To view a full-size version of this map, click here. 

Description of CSO Locations and Potentially Affected Areas

CAM001: Alewife Brook, discharges downstream of Massachusetts Ave Bridge across from Murry Hill Road.

CAM002: Alewife Brook, discharges downstream of Massachusetts Ave Bridge

CAM401A: Alewife Brook, discharges upstream of the confluence with the Little River and upstream of the Route 2 Bridge.

CAM401B: Alewife Brook, discharges upstream of the Massachusetts Ave Bridge.

CAM005: Charles River, discharges downstream of the Eliot Bridge across from Mount Auburn Hospital.

CAM007: Charles River, discharges downstream of the Eliot Bridge across from Hawthorne Street.

CAM009: Charles River, discharges upstream of the Anderson Bridge (temporarily closed).

CAM011: Charles River, discharges upstream of the Weeks Footbridge (temporarily closed).

CAM017: Charles River, discharges downstream of the Longfellow Bridge across from Front Park.

Note: The CSO discharge table below provides details of recent discharges.  Data for CSOs is preliminary and subject to change.  Discharge duration and volume are estimates and are subject to calculation limitations, including meter data reliability, unmonitored downstream conditions such as river level, and MWRA system operations.  See the following links for information on past CSO annual reporting and yearly CSO discharge summaries.  Annual reporting data for 2021 will be published by April 30, 2022.