Officials said the number of outbreaks has increased by 13% each year.
Cryptosporidium, or crypto, can be introduced into a person's system when swimming and swallowing contaminated water, CNN reported.
Crypto can survive in a pool that has the correct level of chlorine for seven days, the CDC said.
What steps can someone take to make sure they don't pass crypto to unsuspecting swimmers?
Avoid swimming for two weeks after having diarrhea and it subsides. But that probably won't happen as experts at the Water Quality & Health Council found that a quarter of people recently surveyed will only wait an hour, not weeks before jumping into a pool, CNN reported.
If you have been diagnosed with cryptosporidiosis, the condition caused by the parasite, clean surfaces with hydrogen peroxide since chlorine bleach has little to no effect on crypto, CNN reported.
For more on cryptosporidiosis, including signs and symptoms, click here.