A new report from the Centers for Disease Control and Prevention (CDC) finds nasty germs that could be lurking in hotel swimming pools. The report, distributed in CDC’s Morbidity and Mortality Weekly Report, took a look at cases from 2000 through 2014 and found that 493 episodes were accounted for, bringing about no less than 27,219 illnesses and eight deaths. Cryptosporidium is a parasite tough enough to survive even in properly maintained pools and was the most common cause of illness. It was responsible for 58 percent of outbreaks, and 89 percent of all illnesses. Cryptosporidium spreads in pool water when someone who is sick with the parasite goes swimming and has diarrhea in the water and then others swallow the contaminated water.

To help stay safe in the pool, the CDC recommends not letting your kids swim if sick with diarrhea, don’t swallow pool water, and before swimming, check the facility’s inspection score.