Public health authorities are warning parents to keep their kids safe this summer from stomach bugs—especially when they're swimming.

During the summer, stomach bugs are more common. More people in the pool means more transmission and more cases.

The aquatic center in Pharr, just about to open up for the summer, has staff with instructions to check the water constantly. They're looking out for infections that can hit you when you least expect it and manage the chlorine, which kills bugs that can make you sick.

"We check the water for chlorine, PH, on the hour, every hour,” said Adam Diaz with the Pharr Parks and Recreation Department.

Health officials say parents need to be on the lookout for stomach bugs, specifically a parasite called cryptosporidium.

"That is a waterborne parasite that is very common in areas that might not be very sanitized,” said Eddie Olivarez, the chief administrative officer at the Hidalgo County Health and Human Services Department. “For example, you get swimming pools that don't have proper chlorine levels, the lakes, the beach, some natural water sources."

Cryptosporidium can also affect your summer plans if you're traveling in another country and drinking their water, or if you eat food that hasn't been properly washed.

It can keep you out of the water and in bed for at least a week.

"You're going to start feeling cramping, stomach pain, vomiting and nausea, some diarrhea,” Olivarez said.

If you feel those symptoms, ask your doctor to check you out.

"Don't drink the water in the swimming pool," Diaz said.