You might want to wear a wet suit while taking a dip in your neighborhood public pool this summer. According to a recent survey in which roughly 1,000 American adults were asked whether they urinate in pools, one in five admitted to doing so. As if that statistic isn’t gross enough, it reflects only the number of people who admitted to peeing in pools. While chlorine kills most waterborne germs, bugs can develop antibodies to the disinfectant and spread rapidly. Additional bacteria carried on human skin, including sweat and fecal matter, raises the risk of E. coli or salmonella contaminating pools. The chances of getting sick are highest at crowded recreational water parks, according to the Centers for Disease Control. Over the past two decades, the CDC has also seen a significant increase in gastrointestinal illnesses caused by swimming in dirty pools across the U.S.