4 Health Hazards in the Water

By Pamela Weintraub, Experience Life

Sharks in the water! Chlorine that seals your contact lenses to your eyes! Antibiotic-resistant bacteria on the beaches! When it comes to recreational swimming, it can be tough to differentiate between overblown fears and more common (and manageable) health hazards.

Swimming is one of summer’s best-loved activities, providing ample fitness benefits in the company of friends — yet it often provokes anxiety. And the truth is, swimming does carry some risks: Open water can carry viral infections from sewage; chlorinated pool water can provoke asthma; and cloudy lakes may contain cyanobacteria, known to carry neurotoxins and cause disease. But with a little awareness, these hazards can be negotiated. By staying alert to red flags and following some simple safety guidelines, recreational swimmers can splash around safely.

Concern: Bacterial and Viral Infections
Source: Oceans, rivers, lakes, pools and hot tubs. In natural bodies of water and outdoor pools, bacterial and viral infections, otherwise known as recreational water illnesses (RWIs), often come from pollution delivered by sewage or rainwater runoff. In indoor pools or crowded beaches, infections may come from other swimmers.

Symptoms: A wide variety of skin, ear, eye and respiratory issues. Gastrointestinal problems, including diarrheal illnesses, are caused by organisms ranging from Crypto (short for Cryptosporidium) and giardia to shigella and E. coli. “Viruses are assumed to be the cause of most waterborne illness, but the specific virus that causes an illness is usually unknown,” says John Wathen, a beach water expert with the U.S. Environmental Protection Agency (EPA) in Washington, D.C.

Avoiding risk: According to David Beckman, director of the Water Program at the Natural Resources Defense Council (NRDC), beachgoers can reduce their chances of getting sick by swimming only at sites where authorities test the water frequently and close the beach or issue an advisory when it is polluted. Healthy strategies include staying out of the water when there are closings or advisories, avoiding swimming near discharge pipes, and keeping dry if you have an open wound. Wathen recommends avoiding beaches for a couple of days after a heavy rain and staying attuned to murky water or foul smells. Indoors or out, make sure that your pool water is properly and adequately treated with an anticontaminant.

Following exposure: Rinse off well. Clean skin abrasions. Dry out your ears. Take a shower and wash swimsuits and towels as soon as possible.

Concern: Chlorine
Source: Swimming pools and hot tubs.

Symptoms: Skin irritation, wheezing, coughing, throat burning, stinging eyes or shortness of breath. Chlorine reacts with organic compounds in various ways that release both waterborne and airborne toxins. In recent studies of children and teens, Alfred Bernard, a toxicologist at the Catholic University of Louvain in Brussels, found that chloramines and haloacetic acids released by chlorine are five times more likely than secondhand smoke to exacerbate symptoms of asthma and respiratory allergies in those already at risk for these conditions.

Avoiding risk: Steer clear of overchlorinated swimming pools (chlorine between 2 and 5 parts per million is considered safe for most). When in doubt, ask pool managers to check the levels of active and combined chlorine in pool water or air. You might also seek out pools treated with alternative disinfectants like copper-silver or ozone, although these may not be ideal for avoiding all RWIs.

Following exposure: If your time in the pool has produced asthma or allergies, treat yourself as you would following any other precipitating cause. Above all, do not go back into the water until you are symptom-free — and limit your time in the pool to minutes, not hours, a day.

Concern: Neurotoxins
In oceans, rivers, lakes and ponds, blue-green cyanobacteria can accumulate when exposed to runoff from phosphorus fertilizer or paper mills, sometimes becoming so dense they coat the water with a green slime.

Symptoms: Some species of cyanobacteria release a neurotoxin so potent that chronic exposure is starting to be traced to neurodegenerative diseases like Parkinson’s and ALS, according to Dartmouth-Hitchcock Medical Center neurologist Elijah Stommel, MD, PhD. Far more common, he says, is brief, acute exposure, which can result in anything from itching and skin rash to illnesses of the GI tract and liver.

Avoiding risk: Stay out of dark or murky waters. “If you see green fluorescent scum on the surface of a pond, don’t go in,” advises Stommel. The smell of rotting eggs may be another sign of cyanobacteria in the water.

Following exposure: As with exposure to RWIs, take a shower and wash swimsuits and towels as soon as you can.

Swimming With Wildlife
When we venture into wild waters, we are entering environments alien to our own: Oceans are home to sharks, rays and jellyfish; rivers and lakes host many species of fish. All kinds of mammals and reptiles inhabit our shores, and insects hover above them, but are we really in danger from wildlife in the places we normally swim — and if so, how can we stay safe?

While most ocean beachgoers view shark attack as the greatest threat to their lives, University of California, Berkeley, coastal oceanographer and researcher Francis James Smith, PhD, coauthor of the Dangerous Beaches Mapping Project, notes that such attacks are extremely rare — only about 75 occur each year worldwide, with 10 resulting in death.

A far more common ocean hazard is the box jellyfish — the free-swimming, colorless animal that can range in size from a couple of inches to 3 feet in diameter. “Box jellyfish use nematocysts in their tentacles to catch their prey,” Smith explains. “Humans can get stung when they come into contact with the tentacles.”

When it comes to aquatic wildlife, rivers and lakes are safer than oceans, according to wildlife and fishery expert Richard Whitman, PhD, of the Lake Michigan Ecological Research Station in Porter, Ind. In fact, most wildlife in U.S. lakes is benign. “I cannot think of any truly dangerous large animal living in those waters,” says Whitman. The most hazardous animal in the nation’s lakes could be the bird flukes, a tiny flatworm that can burrow inside the body, causing swimmer’s itch, he says, adding that lake swimmers face far more danger from land animals living alongside rivers or lakes — for instance, bears, elk, moose or snakes — than from anything in the water.

As with pollution, the best way to avoid dangerous animals when swimming in the wild is vigilance: Visit well-monitored beaches that have lifeguards, and learn about any potential hazards before you venture in. Avoid brackish water with poor visibility. And, when lakeside, avoid areas with high grass or shrubbery that might hide animals. For more water-quality resources and safety tips, see the Web Extra! from Experience Life.

Pamela Weintraub is a senior editor at Discover magazine and author of Cure Unknown: Inside the Lyme Epidemic (St. Martin’s Press, 2008).


Elisa F.
Elisa F4 years ago

Thanks for the info.

mr Crowley
mr Crowley7 years ago


Inez Deborah Altar

My father knew this all the years, this is today´s scourge

Alberta G.

I remember being little and no one thought of polluted water. Just another example of taking something for granted.

Antoinette Reyes
Antoinette R7 years ago

aww the description of neurotoxins reminds me of a horrible sight at redhill park (i think it is called) in rancho cucamonga, ca there is a bunch of fish, turtles and ducks living in murky waters

Kay L.
KayL NOFORWARDS7 years ago

Good, commonsense guidelines. Thanks.

Heidi C.
Heidi L7 years ago

Thanks for the info!

Mervi R.
Mervi R7 years ago

Very interesting, thanks for the info!

Patti Turchon Steigerwald

I am not surprised. OH, MY GOSH !! Makes you think before you drink. YET WATER IS OUR BEST & MOST NEED DRINK. suppose to have nearly a 1/2 gal a day. We are screwing up all God's good stuff. I pray we have the answer to the HUGE oil slick down south.....

Amy Raybourn
Amy Raybourn7 years ago

Thanks for the lesson. I am in constant control of my pool. Now I will be even more viligant.