Combined Sewer Overflow Health Alerts

The public is advised to avoid contact with affected water bodies for at least 48 hours after a sewage discharge or overflow, during rainstorms, and for 48 hours after rainstorms end, due to increased health risks from bacteria or other pollutants associated with urban stormwater runoff and discharges of untreated or partially treated wastewater.  

Combined Sewer Overflows

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 prevents sewage backups into homes and businesses.

When a CSO occurs, notifications to the public are made by the entity responsible for the sewage infrastructure. For surface waters in Boston, these are mainly the Boston Water and Sewer Commission and the Massachusetts Water Resources Authority.

For more information about CSOs and to sign up for CSO notifications for Boston Harbor and Fort Point Chanel, please visit the Boston Water and Sewer Commission’s CSO notification page.

For notifications and alerts for sites on or around the Charles River, please visit the MWRA’s CSO notification page.

Public Health Notifications

State regulations also 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.