The CDC this week revealed that a new study on fecal matter in public pools uncovered a disturbing statistic. Over half of pools tested in the study were found to have E. coli, a marker for fecal contamination.

The study tested pool filters from public pools, looking for genetic material. It found that 58% of the filters tested positive for a strain of E. coli that is normally found in human intestines and in feces. The CDC stated that the study indicates people are either pooping in pools or failing to clean themselves well before entering pools.

“Swimming is an excellent way to get the physical activity needed to stay healthy,” said Michele Hlavsa, chief of the Healthy Swimming Program at the CDC. “However, pool users should be aware of how to prevent infections while swimming. Remember, chlorine and other disinfectants don’t kill germs instantly. That’s why it’s important for swimmers to protect themselves by not swallowing the water they swim in and to protect others by keeping feces and germs out of the pool by taking a pre-swim shower and not swimming when ill with diarrhea.”

The CDC recommends several practices to cut down on pool contamination. Some of the obvious ones include people not swimming if they have diarrhea, showering with soap before swimming, and washing hands after using the restroom or after changing diapers. The agency also recommends taking bathroom breaks every hour, and checking children’s diapers every half-hour. More advanced pool users can check chlorine levels and water PH before swimming. Possibly the best advice the CDC gives, though, is that swimmers should not swallow the water they swim in.