It's not something drivers in Cambridge expected to see: foam covering a busy roadway.
The issue was first spotted in the Fountain Street and King Street area on Thursday night and then occurred again on Friday afternoon.
A *401 caller to CityNews 570 initially reported it looked like bubbles were shooting out of sewer holes.
According to a statement from Mike Parsons, director of environmental services with the City of Cambridge, the foam was a result of a sanitary sewer system issue.
Parsons said the foam was coming up through the lids of some maintenance holes, covering the road and causing a visual distraction.
It was reported that as of Friday afternoon at 2:30 p.m. the foam had stopped and clean-up was underway.
"Staff continue to monitor the scene for any further recurrence," said an e-mail statement from Parsons. "City and regional staff are investigating all possible upstream sources for any likely cause."
Parsons added the city's drinking water has not been affected by the issue and remains safe.
