The Hillsborough County Health Department issued health advisories for three public beaches today.
Elevated levels of bacteria were found in the water at Simmons Park, Picnic Island and Davis Island.
The bacteria is found in animal and human waste and may come from storm water runoff and sewage.
Keely Smith is with the county's health department. She says Tropical Storm Colin is a likely cause.
"Anytime that there is a large storm or tropical storm or even a thunder storm it can stir up the water and it can also cause increased amounts of runoff," Smith said. "So there is a possibility of having the beach advisories issued after a large storm."
The storm also forced the City of St. Petersburg to dump 8.5 million gallons of partially-treated sewage into Tampa Bay.
The sewage from the city's overburdened system was released about a quarter mile off downtown St. Petersburg.
Smith said there's no way to know if that release is the source of the bacteria contaminating Tampa's beaches.
"We know that it does indicate that there's fecal pollution, which it can come from storm water runoff, pets and wildlife and human sewage but the exact source of where the bacteria on our beaches is coming from, there's no way to determine if it came from Pinellas," Smith said.
The health department issues advisories when bacteria levels could put swimmers at risk. The advisories are also posted on the agency's website.
Water quality tests taken on seven beaches in Pinellas found elevated levels of bacteria, but not high enough to issue advisories.