Before you take a dip in the pool this summer, this may change your mind.
The Centers for Disease Control took samples of water in public swimming pools.
Researchers studied the water in pool filters, and found 58 percent of the samples tested positive for E. Coli, a bacteria normally found in feces and the human gut.
Researchers say the findings mean that swimmers are contaminating the pool water, either with what they call "fecal incidents" or by failing to wash feces off their bodies before entering the water.
The CDC is reminding swimmers that chlorine and other disinfectants don't kill germs instantly.
It says people should avoid swallowing pool water, and should take pre-swim showers to keep germs out of the pool.