The MWRA and the Boston Water and Sewer Commission are reporting that "combined sewer outfalls" dumped raw and treated sewage, along with lots of rainwater, into area waterways overnight because of all the rain - but that the flow means people didn't have to worry about sewage backing up into their homes and businesses.
The MWRA explains:
A combined sewer overflow (CSO) occurs when a large storm overwhelms the sewage system causing rainwater to mix with wastewater and discharge to a nearby water body. This relief measure prevents sewage backups into homes and businesses.
The first overflow started at 6:55 p.m. on Wednesday at a pipe into the Mystic in Somerville.
On the off chance you were thinking of going for a swim in one of the rivers or the harbor, the MWRA advises: Don't. At least not for a couple of days.
The MWRA says it's too early yet to say just how much sewage was released into the Charles and Mystic rivers, Alewife Brook and directly into Boston Harbor. It adds that it only tracks releases from its own pipes; Boston, Chelsea, Cambridge and Somerville have their own outfall pipes as well.
BWSC reports most of its CSOs, along Boston Harbor and the Muddy River released sewage into the waterways as well (gold or red on the map indicates overflows):