Chlorine can kill germs in the pool, but it can’t work miracles. At the Centers for Disease Control and Prevention, Michele Hlavsa says the idea that swimming pool disinfectants kill germs instantly is a myth. She says that’s why it’s unhealthy to treat the pool like a toilet, and healthy to shower off any germs before getting in.

Mostly, people just have fun. But Hlavsa notes they can get a variety of diseases.

“They can get gastrointestinal infections, viral meningitis, ear infections – also known as swimmer’s ear – but the most common infection is diarrhea.”

So, she advises, don’t swallow the water, or swim with open sores.