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(NEXSTAR) – If you thought those post-swim red eyes and that “chlorine” smell were due to pool chemicals, the Centers for Disease Control and Prevention has some nauseating news.

The odor and those irritated eyes are instead due to chlorine mixing with the pee, poop, sweat, dirt, skin cells, makeup and deodorant that swimmers bring into the pool, according to the CDC. In fact, a health pool with chlorinated water doesn’t have a strong chemical at all.

In fact, a CDC study that tested public pools found that 58 percent of samples came back positive for E. coli, bacteria found in the human gut and feces.

When combined with pool chemicals, those substances people carry into the pool with them can form chloramines, chemical irritants that can also cause skin irritation, nasal irritation, coughing, asthma attacks and wheezing.

Pool chemicals effectively kill most germs, but some are more persistent. Chlorine also becomes less effective the more it has to neutralize contaminants.

One of those persistent germs is cryptosporidium.

“Cryptosporidium can survive more than 7 days in pool water with 1 ppm free chlorine,” a spokesperson from the CDC’s Waterborne Disease Prevention Branch told Nexstar. “This is partly why Cryptosporidium is the leading cause of outbreaks linked to pools.”

Cryptosporidium generally causes diarrhea, but symptoms can be especially severe for people with weakened immune systems.

The CDC recommends taking the following steps to stay safe at a public pool or hot tub:

  • Try to find any inspection records posted online before going
  • Use test strips (sold at hardware or pool supply stores) to make sure the pH level is 7.2 – 7.8. The free chlorine concentration should be at least 1 ppm in pools and at least 3 ppm in hot tubs/spas. The bromine concentration should be at least 3 ppm in pools and 4 ppm in hot tubs/spas.
  • Can you see the drain at the bottom of the deep end? That’s a sign that life guards will be able to see swimmers clearly.
  • Make sure the drain covers aren’t broken or unsecured.
  • Be sure that there is safety equipment, such as a rescue ring or pole, if a lifeguard isn’t on duty.