The Centers for Disease Control and Prevention is warning of a rise in a parasite that can live for days in swimming pools and water playgrounds, officials said in a report released last week. 

Cryptosporidium, or Crypto, is a parasite spread through fecal matter of infected humans or animals. Cases of Crypto have been rising 13% each year from 2009-2017. 

Crypto causes nausea, vomiting and diarrhea that can last for weeks, according to the CDC. Older people, younger children and those with compromised immune systems are at most risk when they contract the parasite, as it could lead to malnutrition. 

The parasite has an outer shell that makes it tough to kill. Crypto can survive for days in chlorinated water or on surfaces disinfected with bleach. From 2009-2017, 35% of more than 400 Crypto outbreaks were linked to pools, while 15% were linked to cattle and 13% were linked to childcare facilities. 

“Young children can get seriously sick and easily spread Crypto," Michele Hlavsa, chief of CDC’s Healthy Swimming Program, said in a statement. "They don’t know how to use the toilet and wash their hands, or are just learning how. But we as parents can take steps to help keep our kids healthy in the water, around animals, and in childcare.”

To prevent outbreaks of Crypto, the CDC recommends keeping children out of the pool and out of childcare if they have diarrhea and washing hands after coming into contact with animals. You should also avoid swallowing pool water.