(CNN) – Before you head to the pool, listen up. There could be something in the water that could literally turn your stomach.

It’s a parasite called cryptosporidium — or “crypto” for short. It’s spread by feces and the CDC says they’re seeing more and more people come down with it.

In fact, in a report that came out Friday, they say they’ve seen a nearly 13 percent increase every year between 2009 and 2017.

Most people who get “crypto” get it from the pool but you can also get it from lakes and cattle.

They say it can cause quote “profuse, watery diarrhea” for as long as three weeks.

It can be worse for kids, pregnant women and anyone who has a compromised immune system.

So what can you do?

Well, chlorine and filters aren’t enough to keep “Crypto” away. So if you go to the pool, shower after.

And if you know anyone who’s had diarrhea recently, don’t let them in the pool.