The Chicago Park District is working with researchers to find out if dogs are to blame for pollution at Montrose Beach.
They are running DNA tests on dog waste found in water samples from Montrose, Rainbow, and Calumet beaches.
The Natural Resources Defense Council reports Montrose Beach is the most frequently contaminated. The Council researchers want to determine if the waste is coming from the dog beach nearby.
Foster Beach, also next to the dog beach, does not have the same contamination issues.
Gulls are believed to be a big part of the problem, so beach goers are asked to clean up the area when leaving.