Under the surface of your favorite swimming pool, beach, and lakes, hazards too small to be seen by the naked eye might loom.
These bacteria, viruses, and parasites can turn a refreshing plunge into a nasty infection.
"There's a variety of microorganisms that can make recreational activities in water less than fun," said Dr. Stacey Rose, associate professor of infectious diseases at Baylor College of Medicine in Houston. "Microorganisms thrive in every type of water, and infections will impact everyone differently."
Recreational swimming has been linked to outbreaks of Cryptosporidium, Legionella, norovirus, and Giardia.
Those with compromised immune systems or open wounds should not swim in these shared water environments. Those with open wounds could shed harmful bacteria. An infection can lead to diarrhea, skin rashes, ear pain, cough or congestion, and eye pain.
Those who have had diarrhea should avoid swimming in public waters for at least two weeks, Rose said.
"You can shed microorganisms like norovirus or E. coli for several days, sometimes weeks after diarrhea has subsided," Rose said in a college news release. "Children who still wear diapers are at a high risk of spreading these bacteria, so bodies of water designed for babies and toddlers often have higher than usual amounts of fecal matter."
Pools and water parks treat water with chlorine to kill harmful microorganisms, but frequent use by multiple swimmers can introduce new microorganisms or increase levels of those already in the water. This makes chlorine less effective.
Some microorganisms, such as Cryptosporidium, are resistant even to chlorine.
In fresh water and salt water, other hazards exist. In fresh water, that includes Naegleria fowleri, or brain-eating amoeba. Fortunately, it is uncommon.
"A great prevention technique is pinching your nose closed when diving in to prevent water from going directly into your sinuses and infecting you," Rose said.
Swimming in brackish water or in the Gulf of Mexico can put you in contact with Vibrio vulnificus. If you have liver disease or other immune-compromising conditions, you're at highest risk.
Rose offered some preventive tips. Rinse off with a shower after swimming. Buy test strips that analyze chlorine levels, so you can test the water yourself.
Stop if the environment gives you pause, such as smelling something foul in the water, see discolored or cloudy water, or see drainage pipes close to or in the water. Follow proper maintenance and cleaning schedules for your own pools before inviting others to swim.
"Think of swimming hygiene as a two-way street — by taking the right precautions, you protect yourself and in turn protect others," Rose said.
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