Beachgoers are being warned not to swim at three beaches in Quincy and Dorchester because of high bacteria levels.
The Massachusetts Department of Conservation and Recreation on Wednesday posted "No Swimming" signs at Wollaston Beach in Quincy and Malibu and Tenean beaches in Dorchester because of high levels of the enterococci bacteria.
Enterococci is a common gut pathogen in mammals and birds that can cause infections. The bacteria is spread and can contaminate water sources through human and animal feces.
DCR said several water samples from the state-managed beaches showed levels beyond the limits the Massachusetts Department of Health deems acceptable.
A DCR official said that several factors can cause the increased levels, including "stormwater runoff due to precipitation events, fecal accidents in the water by swimmers, or bird and animal waste falling into the water."
The beaches will be closed to swimmers until the bacteria levels fall within the acceptable limits.