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.

Map of Combined Sewer Overflow Locations

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.

Event Date CSO Number Outfall Location Potentially Affected Area  Start Time Stop Time  Duration    Volume (million gallons) Event Rainfall (inches)
09.10.2021 CAM005  Charles River  Downstream of the Eliot Bridge, across from Mount Auburn Hospital  1:16 am - No Activation No Spill No Spill No Spill 0,96"
09.10.2021 CAM401A  Alewife Brook  Upstream of the confluence of the Little River and upstream of the Route 2 Bridge  1:04 am 3:29 am 145 minutes 0.10 0.96"
09.02.2021 CAM007 Charles River Downstream of the Eliot Bridge, across from Hawthorne Street 3:05 am 5:15 am 130 minutes 0.47 4.25"
09.02.2021 CAM001 Alewife Brook  Downstream of Mass Ave Bridge, across from Murry Hill Road 2:45 am 5:45 am 180 minutes 0.06 4.25"
09.02.2021 CAM017 Charles River Downstream of the Longfellow Bridge, across from Front Park 1:35 am 5:15 am 220 minutes 4.43 4.25"
09.02.2021 CAM005 Charles River Downstream of the Eliot Bridge, across from Mount Auburn Hospital 12:07 am 6:00 am 353 minutes 0.29 4.25"
09.02.2021 CAM401B Alewife Brook Upstream of the Mass Ave Bridge 12:15 am 7:30 am 435 minutes 0.18 4.25"
09.01.2021 CAM401A Alewife Brook Upstream of the confluence of the Little River and upstream of the Route 2 Bridge 7:00 pm

6:45 am

705 minutes 2.95 4.25"
09.01.2021 CAM001 Alewife Brook Downstream of Mass Ave Bridge, across from Murry Hill Road 11:26 pm - no activation see 09.02.2021 see 09.02.2021 see 09.02.2021" 4.25"
08.22.2021 CAM005 Charles River Downstream of the Eliot Bridge, across from Mount Auburn Hospital 9:25 am 9:40 am 15 minutes 0.02 0.89"
08.22.2021 CAM401B Alewife Brook Upstream of the Mass Ave Bridge 9:20 am 9:45 am 15 minutes 0.004 0.89"
08.22.2021 CAM401A Alewife Brook Upstream of the confluence of the Little River and upstream of the Route 2 Bridge 9:05 am 9:45 am 40 minutes 0.29 0.89"
08.19.2021 CAM007 Charles River Downstream of Eliot Bridge, across from Hawthorne Street  12:35 pm 1:15 pm 40 minutes 0.20 1.72"
08.19.2021 CAM001 Alewife Brook  Downstream of Mass Ave Bridge, across from Murry Hill Road  12:05 pm  12:50 pm 45 minutes 0.43 1.72"
08.19.2021 CAM005 Charles River Downstream of the Eliot Bridge, across from Mount Auburn Hospital  12:00 pm 1:15 pm 75 minutes 0.10 1.72"
08.19.2021 CAM401B Alewife Brook  Upstream of the Mass Ave Bridge  11:45 am  1:30 pm 135 minutes 0.55 1.72"
08.19.2021 CAM401A Alewife Brook  Upstream of the confluence with the Little River and upstream of the Route 2 Bridge  11:00 am  1:30 pm 150 minutes 1.13 1.72"
08.19.2021 CAM017 Charles River Downstream of the Longfellow Bridge, across from Front Park  11:00 am  12:30 pm 90 minutes 2.43 1.72"
07.27.2021  CAM001  Alewife Brook  Downstream of Mass Ave Bridge, across from Murry Hill Road  No Spill No Spill  No Spill No Spill 0.74"
07.27.2021 CAM005  Charles River Downstream of the Eliot Bridge, across from Mount Auburn Hospital  7:50 pm  8:20 pm 30 minutes  0.04  0.74"
07.27.2021 CAM401B  Alewife Brook  Upstream of Mass Ave Bridge  7:51 pm 8:20 pm 30 minutes  0.08  0.74"
07.27.2021 CAM401A  Alewife Brook  Confluence of Little River, upstream of Mass Ave Bridge  7:45 pm 8:15 pm  30 minutes  0.24 0.74" 
07.18.2021 CAM005  Charles River Downstream of the Eliot Bridge, across from Mount Auburn Hospital 5:15 am  5:30 am  15 minutes  0.02  0.34" 
07.18.2021 CAM401A Alewife Brook Confluence of Little River, upstream of Mass Ave Bridge 5:11 am 5:45 am 34 minutes 0.75 0.34"
07.18.2021 CAM007  Charles River  Downstream of the Eliot Bridge, across from Hawthorne Street 5:00 am  5:30 am  30 minutes  0.24  0.34" 
07.12.2021 CAM005  Charles River Downstream of Eliot Bridge, across from Mount Auburn Hospital 8:30 am 9:00 am  30 minutes  0.02  1.05" 
07.12.2021 CAM401A  Alewife Brook  Confluence of Little River, upstream of Mass Ave Bridge 7:45 am  10:45 am  3 hours  1.72  1.05" 
07.09.2021 CAM401A Alewife Brook Confluence of Little River, upstream of Mass Ave Bridge 12:45 pm 2:13 pm  1.5 hours 0.44 2.53"
07.09.2021  CAM007  Charles River Downstream of Eliot Bridge across from Hawthorne Street 12:10 pm 1:20 pm 1.2 hours 0.68 2.53"
07.09.2021 CAM005 Charles River Downstream of Eliot Bridge across from Mount Auburn Hospital 11:30 am 1215 pm 0,75 hours 0.18 2.53"
07.09.2021 CAM017 Charles River Downstream of Longfellow Bridge, across from Front Park 10:15 am 1:30 pm 3.25 hours 3.31 2.53"
07.09.2021 CAM401B  Alewife Brook Upstream of Mass Ave Bridge  11:30 am 2:50 pm 3.33 hours 0.57 2.53"
07.03.2021 CAM401A Alewife Brook  Confluence of Little River, upstream of Mass Ave Bridge  9:37 pm 9:42 pm  5 minutes  0.07  1.39"
07.03.2021 CAM001 Alewife Brook  Downstream of Mass Ave Bridge, across from Murry Hill Road  Data Unavailable  Data Unavailable Data Unavailable Data Unavailable 1.39" 
07.02.2021 CAM401B

Alewife Brook

Upstream of Mass Ave Bridge 2:00 am 3:30 am 1.5 hours 0.473  2..23"
07.02.2021 CAM007  Charles River Downstream of Eliot Bridge  2:08 am 3:20 am 1.2 hours  0.038   2.23"
07.02.2021 CAM401A  Alewife Brook  Confluence of Little River, Upstream of Mass Ave Bridge  1:29 am 3:30 am 2.0 hours 0.81  2.23"
07.02.2021 CAM001  Alewife Brook Downstream of Mass Ave Bridge, across from Murry Hill Road Data Unavailable Data Unavailable Data Unavailable Data Unavailable  2.23"
07.02.2021 CAM005  Charles River Downstream of Elliot Bridge, across from Mount Auburn Hospital 2:15 am 3:52 am  1.62 hours  2.27   2.23"
07.02.2021 CAM017 Charles River Downstream of Longfellow Bridge, across from Front Park 12:30 am 2:30 am 2.0 hours 2.91  2.23"
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