As pool season is fast approaching, health experts are warning about the spread of a parasitic infection in public pools and water parks. According to the Centers for Disease Control and Prevention, cases of cryptosporidium, also known as “crypto,” have doubled over the past couple of years there have been at least 32 outbreaks in the United States over the last year, compared to just 16 in 2014. The parasite can spread when people swallow something that has come into contact with the feces of a sick person, such as pool water contaminated with diarrhea. Crypto is a highly-contagious parasite that regular chlorine doesn’t kill. It can survive up to 10 days in properly treated water and is the most common cause of diarrheal illness and outbreaks linked to swimming pools or water parks, according to the CDC. Swallowing just a mouthful of water contaminated with Crypto can make otherwise healthy people sick for up to three weeks with watery diarrhea, stomach cramps, nausea, or vomiting, and can lead to dehydration. When responding to a diarrheal incident in the water or a Crypto outbreak, the CDC recommends closing a pool and treating the water with high levels of chlorine, a procedure called hypochlorination.

To protect your family and others from crypto, the CDC recommends the following tips:

Don’t swim or let your kids swim if sick with diarrhea.
If diarrhea is caused by Crypto, wait two weeks after symptoms have stopped before going swimming.
Don’t swallow the water while swimming.
Rinse off in the shower before getting in the water to help remove any germs on your body that could contaminate the pool.
Take kids on bathroom breaks often, and check diapers in a diaper-changing area — not right next to the pool.