Last updated: Jun 17, 2016

Every summer, we hear terrifying stories about people who picked up deadly germs from swimming. Just last year, for instance, a Florida man died after encountering Vibrio vulnificus flesh-eating bacteria in the Gulf of Mexico, and a Minnesota teen died shortly after contracting a brain-eating amoeba from swimming in a lake.

But swimmers, don't panic. Though cases like these pop up each year, they're few and far between. The Centers for Disease Control and Prevention (CDC) says if you avoid swallowing the water and don't swim in lakes deemed unsafe by the Environmental Protection Agency, then you're most likely in the clear.

That said, milder recreational water illnesses are very common. A recent CDC report on public pools wasn’t too reassuring: it found 78.9% of routine inspections identified at least one violation, and one in eight inspections uncovered violations so serious that the pools had to close immediately.

Educate yourself on the four most common ways swimming can make you sick, and what you can do to protect yourself and your family.

Diarrhea

Once water has been contaminated by germs that cause diarrhea, a swimmer only has to swallow a tiny amount to become infected. These germs—such as Cryptosporidium, Giardia, Shigella, norovirus, and E. coli—can be transmitted anytime someone who’s sick with diarrhea (or has been sick in the last two weeks) enters the water. 

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Cryptosporidum (crypto for short), the most common cause of pool-related diarrhea outbreaks, can stay alive for days, even in pools that are treated properly with chlorine and other chemicals. That's why public pools require you to take a shower before you take a dip. To keep the pool safe for everyone, stay out if you've recently been sick to your stomach

Swimming in lakes or rivers that aren’t monitored for safety can also bring on a case of the runs. “It all depends on what’s coming downstream,” says Mindy Benson, nurse practitioner and assistant clinical professor at UCSF Benioff Children's Hospital in Oakland.  Animals in the water can also pass on these germs, Benson adds. “I wouldn’t recommend swimming in backcountry spots you’re not familiar with, especially not with children.”

Diarrheal illnesses transmitted through the water can last two to three weeks and can cause serious, sometimes even life-threatening, dehydration. If you have diarrhea that’s bloody or that lasts five days or more—or if you also have chills or fever—call your doctor. A dry mouth, cracked lips, flushed skin, headache, confusion, or urinating fewer than four times a day are also signs you should get medical attention right away.  

Hot-tub rash

Water that’s contaminated with the bacteria Pseudomonas aeruginosa can cause hot-tub rash, a skin irritation. Germ-killing chemicals like chlorine break down faster in hot water—hence the higher risk posed by hot tubs and the ailment’s nickname—but this bug can also be spread in poorly maintained pools or contaminated lakes. 

The longer your skin is exposed to contaminated water, the more likely you are to get hot-tub rash. “People sometimes think that when they get out of chlorinated water, they’re clean,” says Benson. “But really the safest thing to do is shower as soon as you can.” You can also ask if the hot tub you’re using is checked at least twice a day for proper disinfectant and pH levels, or check the water yourself using pool and hot-tub test strips. ($10, Amazon.)

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Hot-tub rash, which usually appears as itchy, red, bumpy spots or pus-filled blisters, usually goes away on its own in a few days. If a rash lasts longer than that, call your doctor. 

Swimmer’s ear

Otitis externa—or, as it's more commonly known, swimmer’s ear—happens when water gets trapped in the outer ear canal, causing bacteria or fungus to grow. It's more common in kids than adults, and can cause itching, pain, and swelling. In some cases, pus may drain from the ear (ick). You can tell swimmer’s ear apart from a plain old middle-ear infection (super-common in children) by wiggling the outer ear: If it hurts, it’s probably the former. See your doctor if you think you have swimmer's ear—you may need antibiotics to treat it. 

To protect yourself, dry ears thoroughly after swimming with a soft towel, says Benson. You can also tilt your head from side to side and pull gently on your earlobe to help water escape, or run a hair dryer on low heat a few inches away from your ears. Another option? Buy ear drops at the drugstore ($6, Amazon) that can help dry out the ear canal after swimming.

Respiratory problems

Germs that live in hot tubs or pools can also infect people who breathe in steam or mist coming off the water. The bacterium Legionella, which causes the lung infection Legionnaires’ disease, is sometimes spread this way.

Legionella is found naturally in water, especially warm water. Making sure that a pool or hot tub is properly cleaned and disinfected—either by asking or by testing it yourself—can reduce your risk of becoming infected. 

Legionnaires’ disease can cause coughing, shortness of breath, chest pain, fever, chills, and muscle aches. It is usually treatable with antibiotics when diagnosed early, but it can sometimes be fatal. It’s most dangerous to people who are 50 or older, who smoke or have chronic lung disease, or who have weakened immune systems, but everyone should see a doctor if they suspect they’ve been exposed.