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Memorial Day weekend floodwaters and rains from Tropical Storm Bill left a nasty surprise on several Galveston County, Texas, beaches.

During testing Tuesday morning, high levels of fecal bacteria were detected on 17 of the area's 52 beaches, KHOU-TV reported.

High bacterial level warnings are normally issued when fecal matter from farm animals, pets and sewers is washed into Galveston Bay by rainwaters , Ronnie Shultz, director of environmental health programs for Galveston County Health District, told the Houston Chronicle.

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Health officials suggested beachgoers avoid swimming with such high levels present, KFOR-TV said. Federal regulations state waters that test over 104 CFUs (colony-forming units) are considered dangerous, and many of the water samples tested over 140 CFUs.

But Lori Fitzsimmons-Evans of the Galveston County Health District told KHOU healthy adults should be OK. However, she suggested the elderly, children or anyone with open wounds or compromised immune systems steer clear for the time being.

By Tuesday afternoon, only three of the 17 beaches still tested positive for high levels.

MORE ON WEATHER.COM: Tropical Storm Bill - June 2015