Don’t go in the water.

That was one of the taglines for the 1975 summer blockbuster movie, “Jaws.”

However, this summer it might not be sharks you need to worry about.

It could be a tiny parasite that even pool chlorine has a tough time eradicating.

Officials at the Centers for Disease Control and Prevention (CDC) issued a warning today about a water-based parasite with the scientific name Cryptosporidium.

CDC officials say the “Crypto” parasite caused at least 32 outbreaks in 2016, double the 16 outbreaks reported in 2014.

The CDC reports that almost 750,000 people a year in the United States become ill from the Crypto organism.

There’s no data on how many people were sickened specifically in last year’s 32 outbreaks.

However, the 2016 outbreak in Arizona made at least 352 people sick. The outbreak last year in Ohio made more than 1,900 people ill.

While the CDC is certainly not making a Jaws-like announcement, agency officials still issued their summertime caution.

“Anytime there is an infectious bacteria outbreak, there’s always a concern,” Dr. Dana Hawkinson, an infectious disease specialist at the University of Kansas Health System, told Healthline.

Read more: Get the facts on parasite infections »

A three-week illness

CDC officials said they don’t know if the rise in Crypto outbreaks is due to more infections or better reporting techniques.

Hawkinson said it’s probably a combination of both.

Either way, the Crypto parasite is definitely one to avoid.

People become infected by coming into contact with feces, food, or water contaminated with the parasite.

In a pool or water park, swallowing contaminated water is the easiest way to get infected.

The parasite can make a person sick for as long as three weeks.

Symptoms include diarrhea, stomach cramps, nausea, and vomiting. These symptoms can lead to dehydration.

Crypto is the most common cause of diarrheal illness linked to pools and water parks because it’s not easily killed by chlorine.

The bug can survive for up to 10 days in properly treated water.

Read more: Chipotle outbreak highlights how easily norovirus can spread »

How to avoid getting sick

CDC officials have issued a number of safety precautions to help swimmers avoid becoming infected with Crypto.

The first is to avoid swallowing water while swimming.

The second is not to swim or let your children swim if they have recently suffered from diarrhea.

Officials also urge parents to make sure their children have bathroom breaks and to check the diapers of young children before taking them in the pool.

They also advise swimmers to rinse off before entering a pool or water park to help remove germs on the body.

CDC officials are also urging pool and water park owners to close their facilities after a “diarrheal incident” and treat the water with high levels of chlorine in a process known as hyperchlorination.

Hawkinson noted the CDC advice is useful, but he added that even with precautions there’s still a chance of getting sick.

“A lot of this is out of your control,” he said. “It’s hard. It’s spring, almost summer. A lot of people want to go swimming.”

Hawkinson did say that most healthy adults who get the Crypto illness don’t require treatment and eventually recover without hospitalization.

Small children, older adults, and people with compromised immune systems might require some form of treatment.

He added that diarrhea can be caused by many ailments, so don’t necessarily assume it’s the Crypto parasite if someone in your family develops diarrhea.

Read more: The most dangerous epidemics in U.S. history »