The Mystic River in May 2018. (Photo: Aslam Karachiwala via Flickr)

For the third time this year, people are warned to avoid contact with local bodies of water due to the presence of sewage in stormwater overflow.

Humans and pets should stay away from Alewife Brook and parts of the Mystic River through Tuesday, according to Cambridge’s public health department.

Releases of mixed stormwater and sewage – known as a combined sewer overflow – are needed to prevent contaminated water from backing up into homes, businesses and city streets. Overflows lasting more than two hours, which triggers public notifications, occurred in Alewife Brook Reservation in North Cambridge at 11:20 p.m. and ended at 1:47 a.m. and at 11:50 p.m. and ended at 1:58 a.m., officials said.

Affected areas may include the Alewife Brook and Little River in Cambridge, Somerville, and Arlington, as well as the Mystic River from the intersection of Alewife Brook Parkway and Mystic Valley Parkway in Somerville to the Fellsway/Route 28 bridge in Medford near the Mystic River State Reservation.

Contact with the water can make you and your pets sick, health officials said, calling for people to avoid paddle boarding, boating, fishing or other activities that could lead to contact. 

There was another two-day warning starting Jan. 26 about contact with water potentially tainted by an overflow, and then March 14.

Major work is underway to prevent the overflows; residents from more than a half-dozen communities learned a new timeline for the work at a Dec. 15 meeting organized by Cambridge and Somerville governments and the Massachusetts Water Resources Authority. A draft plan due by June 2023 and a final plan due by December 2023 have been delayed by three years for more public input and analysis, health officials said.

This post took significant amounts of material from a press release.