Pool parasites? One swim can leave you sick for weeks, experts say

According to Catherine Roberts, a health editor with Consumer Reports, pools can contain E Coli, giardia, campylobacter and norovirus. All those can make swimmers sick, but the most common culprit is cryptosporidium, or crypto for short.

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Crypto is spread through fecal matter, and even a small amount can contain millions of germs.

Regular levels of chlorine won't kill crypto. It can survive in a well-maintained pool for up to 10 days.

The Centers for Disease Control and Prevention says swallowing even a mouthful of water infected with crypto can lead to weeks of diarrhea, nausea and vomiting.

To protect yourself and your family, make sure anyone who swims in your pool follows some guidelines.

"Anyone who is experiencing diarrhea or has been sick should not swim,” Roberts said. “Have people take a shower or at least rinse off before they swim."

And make sure kids take frequent bathroom breaks to reduce the risk of accidents. That goes for babies as well.

“Those swim diapers are not foolproof,” Roberts said.

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Pool experts say if fecal matter goes get into the pool, don't take any chances.

"Everybody out of the water,” said Vincent Groppa of Consumer Reports. “Shut it down."

The only way to effectively kill crypto, he says, is to have a professional super-chlorinate the water and then slowly bring it back to normal levels again -- a process that can take at least 8 hours.

“It's like a supergerm, you know, so that's the only way to take it out of the pool," Groppa said.

If you have crypto, the CDC says you should wait a full two weeks after any stomach issues stop before getting back in a pool.