It's called Cryptosporidium or crypto, and it is spread by feces.
A report released on Friday said that there's a nearly 13 percent increase every year between 2009-2017.
The parasite can spread when those who have been infected and are experiencing diarrhea go swimming. Others swimming in the contaminated water can get the parasite when they ingest the water.
Patients who become ill with the parasite experience diarrhea for weeks along with pain in the abdomen and a low-grade fever. People with weakened immune systems can become severely ill and could die.
The parasite is the leading cause of diarrhea outbreaks linked to water, according to the CDC. The most common place that Cryptosporidium spreads is at swimming pools and water playgrounds, but it can also spread through contact with cattle and at daycare. Because of this, the CDC encourages everyone to wash their hands after touching cattle, and they recommend keeping your child home from childcare settings if they are having diarrhea.
Pool keepers are told to chemically shock any pool that is suspected or is contained with Crypto.
Parents are urged to avoid taking their children to the pool if they are sick with diarrhea. Swimmers are asked to swim with their mouths closed.
SEE ALSO: Gross! Pool smell comes from chemicals breaking down urine, fecal matter