Is That Water Safe to Swim in? What to Know About Beach Contamination

In recent weeks, floods in the Northeast have led to dozens of beach closures. Heavy rainfall and flooding increase the risk that water will be contaminated with disease-causing pathogens that people can accidentally ingest while swimming.

One recent study estimated that 57 million illnesses each year are the direct result of people swimming in contaminated oceans, lakes, rivers and ponds in the United States. But exact numbers are hard to come by, in part because people don’t tend to report swimming-induced illnesses to health authorities, said Michele Hlavsa, chief of the Centers for Disease Control and Prevention’s Healthy Swimming Program.

This doesn’t mean we should all stop swimming, though — it just means that there are certain situations and warnings to look out for.

“I have a 6-year-old and an 8-year-old, and we go swimming all the time,” Ms. Hlavsa said. It’s all about making smart decisions, she added.

This summer, with its myriad flash floods, swimming has been a bit riskier than usual in certain parts of the country. That’s because heavy rainfall can sweep chemicals, wildlife excrement and manure into waterways, contaminating them.

The problem can be exacerbated in urban areas. “We have roads, parking lots, big-box stores, sprawling development, so that storm water can no longer percolate through the soil the way nature intended,” explained John Rumpler, the clean water director at the nonprofit organization Environment America. Instead, it flows directly into the water.

In addition, heavy rainfall (and severe weather like hurricanes and tropical cyclones) can cause sewage overflows that “release raw sewage and polluted storm water into our rivers, lakes and streams,” Mr. Rumpler said.

According to a recent report from Environment America, 55 percent of the 3,192 beaches around the country that were regularly tested for potential contamination by government researchers in 2022 had potentially unsafe levels of bacteria on at least one testing day. One out of every nine beaches had potentially unsafe bacterial levels on a quarter of all testing days.

There are a few major causes of swimming-related illnesses. One is norovirus, which causes nausea, diarrhea and vomiting for several days, Ms. Hlavsa said.

Cryptosporidium, a parasite, is another common cause of gastrointestinal illness, along with the bacteria E. coli, said Victoria Lynch, an environmental epidemiologist at the Columbia University Mailman School of Public Health.

Some pathogens — such as harmful algae blooms — can also cause rashes, Ms. Hlavsa said.

Swimming-induced illnesses may go away on their own, but “if you’re getting dehydrated and you can’t keep your fluids down, or you’re constantly in the bathroom, whether it be vomiting or having diarrhea, you should definitely be contacting your health care provider,” Ms. Hlavsa said. She recommended that people with weakened immune systems talk to their doctors if they experience gastrointestinal symptoms after swimming.

Ms. Hlavsa suggested checking online to find out if a swimming area is under advisory — which means that people can swim in it but are advised not to — or has been closed for health or safety reasons. This CDC page includes links to each state’s water monitoring divisions. Beaches that are closed or under advisory should also be posted with signs.

But each state manages swimming safety differently, so there is no consistent rating system or signage to look out for. “It’s totally going to depend on the jurisdiction,” Ms. Hlavsa said.

The biggest rule of thumb is to avoid swimming immediately after heavy rainfall. “If there has been heavy rain and flash flooding, I’m not going to go in recreational environmental water for several days,” Dr. Lynch said.

If you know that your swimming area is near a sewer overflow discharge point, you may want to wait 72 hours before swimming, Dr. Lynch said. Many states maintain online maps of these locations that you can find by searching online for “combined sewer overflow” and the name of your state.

If you see a pipe releasing water near your swimming site, that’s certainly a warning sign, Ms. Hlavsa said. Especially murky water is another red flag.

Don’t swallow water or fill your mouth with it and then spit it out, Ms. Hlavsa said. And avoid getting water in open wounds from injuries, recent surgeries, or recent piercings. Otherwise, the wound is “going to be a nice way for germs to enter in and cause infection,” she added.

What if you’re desperate for a swim but not sure if the water is safe? Dr. Lynch suggested briefly dipping your body in without getting your head wet, which reduces the chance that you’ll swallow potentially contaminated water.

“It’s really important that you can cool off when it’s oppressively hot,” she said.

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