Before you go swimming in a public pool this summer, health officials want to offer one piece of advice: Don’t drink the water! If for some reason you end up swallowing some (even just a mouthful), don’t be surprised if you end up sick for weeks with unpleasant symptoms such as watery poop and vomiting.

This advice comes after a report revealing the common diarrhea-inducing parasite, known as “Crypto,” caused at least twice as many swimming pool and water park outbreaks in 2016 than it did two years prior, according to the Centers for Disease Control and Prevention.

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There were 32 outbreaks reported in 2016, according to data in CDC’s Morbidity and Mortality Weekly Report, compared to only 16 in 2014. People in Ohio suffered the most Crypto-related illnesses with 1,940 becoming sick in 2016. The increase in cases may be due to better reporting and laboratory methods, but officials aren’t exactly sure.

Even if a pool is properly maintained, Crypto can still pose a challenge, as it’s able to survive up to 10 days in clean water. The pesky parasite can also continue to thrive after being soaked with standard levels of chlorine. The way people can become sick is if they swallow water that’s been in contact with feces of a sick person.

Although pool water may appear clean, it’s quite common for it to be contaminated with poop. About 1 in 4 adults say they would swim if they had diarrhea, according to a survey by the Water Quality and Health Council.

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“To help protect your family and friends from Crypto and other diarrhea-causing germs, do not swim or let your kids swim if sick with diarrhea,”said Michele Hlavsa, chief of CDC’s Healthy Swimming Program. “Protect yourself from getting sick by not swallowing the water in which you swim.”

In their report, the CDC lists a number of ways to protect yourself and those around you from getting sick from the germs that cause diarrhea:

-Don’t swim if you’re sick with diarrhea.

-If diarrhea is from Crypto, wait two weeks after symptoms disappear before swimming again

-Don’t swallow pool water

-Take a shower before getting in the water

-Take children on bathroom breaks. If they wear a diaper, check it in a diaper-changing area and not near the pool.

If the water becomes infected with Crypto, the CDC recommends closing the pool and treating the water with very high levels of chlorine that are harmful to swim in.

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