Most of the time it is safe to boat on the Mystic. But when sewage is discharged into waterways during heavy rain events—known as a Combined Sewer Overflow, or CSO—it can be dangerous.
A combined sewer overflow (CSO) occurs when a large storm overwhelms the sewage system causing rainwater to mix with wastewater and discharge to nearby waterbodies--in our case, the Mystic River and Alewife Brook. The Massachusetts Water Resource Authority (MWRA) owns the CSO outfalls that discharge to the Charles and Mystic Rivers, Alewife Brook, and Boston Harbor. The cities of Boston, Cambridge, Chelsea and Somerville manage their own combined sewer outfalls and CSO reporting. To see where all CSO outfalls are located, download this map of MWRA and community CSO sites.
How do you know when it’s safe to boat?
First and foremost--we recommend not going out on the water within 48 hours of heavy rainfall (at least 1 inch of rain).
During the Spring-Fall, use MyRWA’s Daily Boating Advisory to determine whether or not it’s safe to boat. You can also get the boating advisory updates on Twitter at @SafeMystic.
Sign up for CSO alerts from the MWRA. The process is easy--create an account with your email address and sign up for CSO discharge notifications.
You can also review CSO data for Boston, Somerville, Cambridge and Chelsea prior to going out.
Lastly, support House Bill 4921, “An act promoting awareness of sewage pollution in public waters.” This bill would require Massachusetts sewage treatment plants to alert the public in a timely manner whenever a CSO occurs—currently not required. Learn more, including what you can do to help, here.
The good news is that despite the occasional CSO discharges, the Mystic River and Lakes have earned an A- from the US EPA based on the levels of bacterial contamination found in samples taken monthly from numerous sites throughout the watershed. 98% of the time it is safe to boat in these locations.You can read more about the MyRWA water quality sampling program and the EPA’s report card for the Mystic here.
Learn more about water quality and CSOs in the Mystic with this “Ask Me Anything” interview with our Watershed Scientist here:
