Combined Sewer Overflow Health Alerts

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. 

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.   

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.  

• Massachusetts Water Resources Authority outfall MWR203 at the Prison Point facility experienced a treated discharge or overflow that started on Sunday, September 27, at 8:31 a.m. and ended at 3:42 p.m., creating a potential public health risk. This event impacts the Inner Harbor. This advisory will expire 48 hours after the overflow ends. 
• Massachusetts Water Resources Authority outfall MWR215 at the Union Park CSO Storage and Treatment Facility experienced a treated discharge or overflow that started on Sunday, September 27 at 9:03 a.m. and ended at 3:34 p.m. creating a potential public health risk. This event impacts the Fort Point Channel, Downtown, and South Boston waterfront. This advisory will expire 48 hours after the overflow ends. 
• Boston Water and Sewer Commission outfall BOS065 in the Fort Point Channel experienced a discharge or overflow that started on Sunday, September 27 at 11:50 a.m. and ended at 2:10 p.m., creating a potential public health risk. This event impacts the Fort Point Channel, Downtown, and South Boston waterfront. This advisory will expire 48 hours after the overflow ends. 
• Boston Water and Sewer Commission outfall BOS070 in the Fort Point Channel experienced a discharge or overflow that started on Sunday September 27 at 9:05 a.m. and ended at 3:30 p.m., creating a potential public health risk. This event impacts the Fort Point Channel, Downtown, and South Boston waterfront. This advisory will expire 48 hours after the overflow ends. 

For more information about CSOs and to sign up for CSO notifications for Boston Harbor and Fort Point Channel, 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.