Somerville Reports Sewer Overflow Into Mystic River

SOMERVILLE, MA – Somerville reported a combined sewer overflow into the Mystic River Monday morning.

The overflow began around 10:53 p.m. on Sunday from the permitted CSO outfall MWR205 located near the Patrick Sullivan Memorial Fishing Hole and ended early Monday morning at 1:46 a.m.

The discharge will likely affect water bodies downstream of the Amelia Earhart Dam, according to the city's notice.

“The CSO discharge consists of partially treated sewage and waste. Avoid contact with these water bodies for 48 hours after the discharge or overflow ceases due to increased health risks from bacteria and other pollutants,” an overflow notice said.

A combined sewer overflow (CSO) occurs when a large rainstorm overwhelms the combined sewage system causing stormwater to mix with wastewater (or sewage) and discharge to a nearby river or lake. These events occur occasionally after heavy precipitation and create unsafe conditions in affected waterways.

Like all cities and towns in Massachusetts, Somerville began reporting sewer overflow incidents in July 2022 under a new state law.