The city's Health Department has issued an advisory warning swimmers not to go in the water at Orchard Beach because of high bacteria levels.
The Health Department posted signs outside of the beach entrance Thursday, and made verbal announcements over the intercom system warning swimmers of the restriction.
Water quality testing performed by the Health Department showed high levels of enterococci bacteria in the water.
They say coming in contact with the bacteria may cause people to suffer respiratory infections, vomiting and diarrhea.
The Health Department says children, pregnant women and the elderly should be especially careful because they are at higher risk of illness.
There is no word yet on when the advisory will be lifted.