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Hey, great news, everyone. It's finally starting to warm up (at least here on the East Coast and in South Dakota), which means it's almost time to open up those swimming pools. And we'd recommend you get to the pool quickly, before all of the other swimmers contaminate it with fecal bacteria.

According to data just released by the Centers for Disease Control, on any given day, in any random pool, there are 58 percent odds that the water in which you're swimming — the water that's swishing around in your mouth and getting in your eyes — contains E. coli. In the view of the CDC, this "indicates that swimmers frequently introduced fecal material into pools and thus might transmit infectious pathogens to others."

The study includes other choice quotes. Like:

Escherichia coli, a fecal indicator, was detected in 93 (58%) samples; detection signifies that swimmers introduced fecal material into pool water. Fecal material can be introduced when it washes off of swimmers' bodies or through a formed or diarrheal fecal incident in the water.

Relaxing, right?

It gets worse. The researchers looked at samples from a variety of different sources, allowing them to assess how common fecal and other bacteria were for pools meeting several different criteria.

To summarize that chart:

  • Indoor and outdoor pools are equally contaminated with E. coli, but outdoor pools are more contaminated overall.
  • Municipal pools are the worst.
  • Pools where kids are the primary users are the dirtiest, for obvious reasons. But the CDC still spells it out: "This finding might reflect differences in the number of swimmers who are either diapered children or children learning toileting skills."
  • If a pool has a sign warning people who are suffering from diarrhea not to swim, that makes it slightly better. So consider this a blanket warning: If you have diarrhea, please do not go swimming.

And, by the way, we're talking about filtered, chlorinated pools. The most effective treatment was chlorine plus ultraviolet light radiation — which dropped the presence of microbes to only 71 percent.

There are some important caveats. One is that the study was conducted only in the Atlanta metropolitan area, so it's possible that other places are cleaner. (In 1998, contamination at a waterpark near Atlanta sickened 26 children, resulting in one death.) The CDC doesn't think the city is an outlier:

[T]he incidence of RWI outbreaks of acute gastrointestinal illness throughout the United States suggests that swimmers frequently introduce fecal material and pathogens into recreational water throughout the country.

Another caveat is that the contamination could have come from other warm-blooded animals. If you saw a bunch of raccoons swimming around in the pool, you should avoid it in that case, too.

It is up to us, the swimmers, to alleviate the problem. One thing you can do is to shower before swimming, with soap. And the other thing is to not go swimming if you have diarrhea. Doesn't matter if there's no sign at the pool warning against it. Just trust us on this.

This article is from the archive of our partner The Wire.

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