If you're looking forward to spending hot summer days by the pool, this may change your mind.
Researchers looked at samples of pool filter water 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 the pool.