“It is time to stop treating the swimming pool as a toilet,” Hlavsa told NBC News. “Nowhere else except for the pool is it acceptable to poop in public or pee in public. In other places if we did this in public, we’d be arrested.”

CDC and county health officials tested the pools in four Florida counties last summer for the study. They got water out of the pool filters and ran tests for microbes – especially E. coli, which lives inside the bodies of animals and which is carried in feces. If E. coli is somewhere, it likely got there via feces.

“Escherichia coli, a fecal indicator, was detected in 93 (58 percent) samples; detection signifies that swim­mers introduced fecal material into pool water,” Hlavsa’s team wrote in CDC’s weekly report on disease and death.