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Boston Harbor and Massachusetts Bay
Massachusetts Water Resources Authority

MWRA SSO Reporting

A Sanitary Sewer Overflows (SSO) is an unintentional discharge of wastewater to the environment prior to reaching a treatment facility. SSOs can occur on infrequent occasions 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. During such events, flow may be discharged to local receiving waters, without treatment, as a last resort to reduce the risk of sewage backing up into homes and businesses.

Public health officials recommend avoiding contact with receiving waters for up to two days after SSO discharges have ended. For more information about SSOs and how to help prevent them, click here.


Map of MWRA SSO sites

How to use this map:

  1. Click on a radio button to view SSOs occurring within a specified time period.
  2. Click on individual markers to view more detail. Past events include links to detailed SSO reports. Additional information will appear in the popup window if multiple events occurred during the selected period.
  3. If there are no SSO events during the selected period, the map will display no markers.

Note: SSOs displayed on map have been reported to the Department of Environmental Protection by MWRA, this map does not include SSOs that may occur outside of the MWRA system.


Select SSO events to display:
* *
SSOs active within the past two days appear as red markers     and older events are yellow    .

*Information is preliminary and is subject to change.

The map above displays SSOs occurring only within the MWRA system and does not include SSOs for community systems.  For additional SSO information, see:

DEP background on SSO regulations
DEP searchable reportable release site list
Boston Water and Sewer (BWSC) SSO notifications