Legionnaires' Disease From Lake Swimming: What to Know

Lake Shore Park, Northern Ohio's Vacation Spot is very popular for picnicking and boating. Curt Teich Curteichcolor 3-

Yes, you can catch Legionnaires' disease from a lake, although it's rare. The bacteria behind it, Legionella, live naturally in fresh water and can multiply in warm, still shallows. You get sick by breathing in contaminated droplets or mist, not by swallowing water, and symptoms usually start within two weeks.

This matters most if you're over 50, smoke, or live with a long-term illness, and for anyone caring for an older relative who swam recently and now has a fever and cough that won't clear.

Key takeaways

  • Legionnaires' disease is a serious pneumonia caused by Legionella bacteria, usually linked to building water systems but occasionally to natural fresh water.
  • Infection comes from inhaling tiny water droplets. Drinking or swallowing lake water is not the usual route.
  • Symptoms look like flu or other pneumonia and typically appear 2 to 14 days after exposure.
  • Older adults, smokers and people with weak immune systems face the highest risk of severe illness.
  • If you get a fever and cough after swimming, tell your doctor about the swim. That detail can change which tests they order.

What happened in the Iowa lake case?

The case was published as a medical report. A 77-year-old man who had swum in a lake in Iowa during a summer trip arrived at a hospital in Winnipeg weeks later with a fever, a cough and repeated falls. The falls weren't from tripping. He was so weak and exhausted that his legs gave out.

His blood tests showed a high white blood cell count, a sign of active infection, and raised creatine kinase, an enzyme that leaks out when muscle tissue breaks down. Muscle breakdown can put strain on the kidneys, which is one reason doctors take it seriously. He was started on broad antibiotics but didn't improve as expected.

A bronchoscopy, where doctors pass a thin camera into the airways to take samples, came back negative for Legionella. That's a known trap: once someone has had antibiotics, cultures often miss the bacteria. A urine antigen test finally confirmed Legionnaires' disease. Doctors switched him to an antibiotic that targets Legionella well, and within four days he no longer needed extra oxygen. He went home to recover.

The lesson is practical. A routine summer swim weeks earlier was the clue that pointed to the right test, and the right test led to the right treatment.

What is Legionnaires' disease and how does it spread?

Legionnaires' disease is a lung infection, a form of pneumonia, caused by Legionella bacteria. Most outbreaks trace back to human-made water systems where water sits warm: cooling towers, hot tubs, large plumbing systems in hotels and hospitals, and decorative fountains. The bacteria grow best in warm water and in biofilm, the slimy layer of microbes that coats pipes, rocks and sediment.

Lakes, rivers and streams naturally carry small amounts of Legionella. Usually the levels are too low to cause illness. Risk rises when conditions let the bacteria multiply, such as late summer heat, shallow coves with little water movement, and lots of biofilm on rocks and plants.

The key point is how it gets into your body. You breathe in fine droplets or mist that contain the bacteria. Splashing, diving, jet skiing or playing in agitated shallow water can create that mist. Most healthy people who are exposed don't get sick, and Legionnaires' disease doesn't usually pass from person to person.

There's also a milder illness from the same bacteria called Pontiac fever. It causes fever and muscle aches without pneumonia and usually clears on its own within a few days.

What symptoms should you watch for after swimming?

Symptoms typically start 2 to 14 days after exposure, according to the CDC, and sometimes later. By then, most people have forgotten about the swim. Watch for:

  • Fever, which can be high
  • Cough, dry at first and later bringing up mucus
  • Shortness of breath or chest pain when breathing
  • Muscle aches, headache and unusual tiredness or weakness
  • Confusion, especially in older adults
  • Nausea or diarrhea, which some people get alongside the chest symptoms

The combination to take seriously is fever plus breathing symptoms that aren't getting better after a few days, particularly in someone older or with a health condition. In older people, the first sign may be something that doesn't look like a chest infection at all, like new confusion or falls, as in the Iowa case. Similar stories happen with other uncommon infections; for example, a woman's months of unexplained flu-like symptoms turned out to have a cause nobody suspected at first.

Who is most at risk of severe illness?

Anyone can get Legionnaires' disease, but some people are much more likely to become seriously ill:

  • Adults aged 50 and older
  • Current and former smokers
  • People with chronic lung disease such as COPD or emphysema
  • People with weakened immune systems from illness or medicines such as steroids, chemotherapy or transplant drugs
  • People with diabetes, kidney failure or liver failure
  • People with cancer

Diabetes deserves a mention because high blood sugar makes it harder for the immune system to fight bacterial infections. If you live with diabetes or prediabetes, keeping your blood sugar steady is part of protecting yourself from infections in general, not only from this one.

Healthy younger adults can still get sick, especially after heavy exposure or when diagnosis is delayed. Age and health status mostly change how severe it becomes.

Which other lake infections are worth knowing about?

Legionella isn't the only freshwater germ that can turn a swim into a medical problem. This table shows the main ones, how they get in and what to do differently.

GermHow it gets inMain illnessWhat helps
LegionellaBreathing in mist or dropletsPneumonia (Legionnaires' disease) or milder Pontiac feverAvoid splashing in warm, stagnant shallows; report the swim if you get a fever and cough
Naegleria fowleri (amoeba)Water forced up the noseA rare, usually fatal brain infectionHold your nose or use nose clips when jumping or diving into warm fresh water
Cryptosporidium and Giardia (parasites)Swallowing waterDiarrhea, cramps and nauseaTry not to swallow lake water; don't swim when you have diarrhea
Vibrio (bacteria)Open wounds, mainly in salty or brackish waterWound infections that can turn severeStay out of the water with cuts, scrapes or fresh tattoos

Naegleria fowleri is extremely rare but frightening because it is almost always fatal. It lives in warm fresh water and enters through the nose, usually during jumps, dives or dunking. Cases have mostly come from southern US states, though some have occurred further north, and at least one case was linked to a lake in Iowa. You cannot get it by swallowing water.

If you're curious about how other unusual parasites end up in the body, our piece on a brain worm diagnosis after unexplained headaches shows how travel and exposure history again proved to be the missing clue. And if a cut gets infected after a dog lick or a swim, take it seriously; the story of a man who died after a dog licked his wound is a reminder that small wounds can let dangerous bacteria in.

How can you lower your risk without giving up lakes?

You don't need to stop swimming. Open water is good for body and mind, and the risk of any of these infections on a given day is very low. People who enjoy cold water swimming actually face lower risk from warm-water germs like Legionella and Naegleria. A few habits make the biggest difference:

Before and during your swim

  • Check for posted advisories, beach closures or algae warnings, and follow them. They exist because someone found a problem.
  • Be more cautious in late summer when the water is warmest, especially in shallow, still coves.
  • Avoid areas with scummy water, visible algae blooms or a strong smell.
  • Hold your nose or use nose clips when you jump or dive into warm fresh water, and keep your head above water in warm shallows.
  • Try not to swallow lake water.
  • Stay out of the water if you have an open cut, a fresh tattoo or a recent piercing.

After your swim

  • Shower after swimming, and clean any scrapes you picked up with soap and water.
  • For the next two weeks, notice any fever, cough, breathlessness, unusual weakness or confusion.
  • If symptoms start, tell your doctor about the swim, where it was and when. Don't assume they'll ask.

A common mistake is treating a high fever and cough in an older parent as "just a bad flu" and waiting it out at home. When the person is over 50 or has a chronic illness, it's better to get checked early.

How is Legionnaires' disease diagnosed and treated?

Doctors usually start with a chest X-ray to confirm pneumonia, then test specifically for Legionella. The most common tests are a urine antigen test and a culture of a sample from the lungs, such as coughed-up mucus or a bronchoscopy sample. The urine test is quick and isn't thrown off by antibiotics in the same way cultures can be, which is exactly why it caught the diagnosis in the Iowa case.

If you or someone you're helping is in hospital with pneumonia that isn't improving, and there was a recent lake swim, hot tub, cruise or hotel stay, it's reasonable to ask the team whether a Legionella test has been done. You're not second-guessing them. You're giving them context they may not have.

Treatment is with antibiotics that work well against Legionella. Most people recover, though some need hospital care and recovery can take weeks. Older adults and people with serious health problems can develop complications such as respiratory failure, kidney problems or septic shock, which is why early diagnosis matters.

Frequently asked questions

Can you get Legionnaires' disease from swallowing lake water?

Usually not. Legionnaires' disease spreads when you breathe in small droplets or mist containing the bacteria, so splashing and spray matter more than swallowing. Rarely, water that goes "down the wrong way" into the lungs while drinking can cause infection, mostly in people who have trouble swallowing. Swallowing lake water carries other risks, such as stomach bugs from parasites.

Is it safe to swim in lakes in the summer?

For most people, yes. Serious infections from lake swimming are rare. You can lower your risk by obeying posted advisories, avoiding warm, stagnant shallows and algae blooms, keeping water out of your nose when jumping in, not swallowing water and staying out with open wounds. People over 50 or with weak immune systems should be a bit more cautious.

How long after swimming can Legionnaires' symptoms appear?

Symptoms usually appear 2 to 14 days after exposure, and occasionally later. Because of that delay, people often forget about the swim by the time they feel ill. If you develop a fever with cough or shortness of breath within about two weeks of swimming, mention the swim to your doctor so they can consider testing.

What to do next

  1. Before your next lake trip, check the local health department or park website for advisories.
  2. Pack nose clips if you or your kids like to jump or dive into warm fresh water.
  3. If you're over 50, smoke or have a chronic illness, make a mental note of swim dates so you can share them with a doctor if you get sick.
  4. Share the symptom list above with older family members who swim, and agree that a fever with cough means a call to the doctor.

See a doctor promptly if you develop a fever with cough, shortness of breath or chest pain within two weeks of swimming, or if an older person becomes unusually weak, confused or starts falling. Seek emergency care for severe breathlessness, blue lips, a sudden severe headache with stiff neck after freshwater swimming, or confusion that comes on quickly.

This article is for general information and is not medical advice.

Sources

Last reviewed: October 2026.

Comments

Post a Comment

Popular Posts

Muscle Gain Diet: What Actually Works, Kept Simple

Image
To build muscle, most people who lift regularly need about 1.4 to 2.0 grams of protein per kilogram of body weight a day, spread over meals of roughly 20 to 40 grams each, plus enough total food to fuel training. Add consistent strength training and decent sleep, and that covers most of the results. Everything else is fine-tuning. This guide is for anyone who has started lifting and feels buried in conflicting advice about meal timing, shakes and supplement stacks. Here's the short, evidence-based version. Key takeaways The International Society of Sports Nutrition (ISSN) says 1.4 to 2.0 g of protein per kg per day is enough for most exercising people building muscle. Spread protein across the day, about 20 to 40 g per meal, every 3 to 4 hours. Exact timing around your workout matters less than total daily intake. Eating before or after training both work. Creatine monohydrate is the best-supported supplement. Protein powder is a convenience, not a requirement. If you...
Read more

Top 10 Exercises to Help You Sleep Longer and Better

Image
The best exercises for sleep are the ones you'll do most days: brisk walking, yoga, swimming, cycling, strength training and gentle evening stretching all have research linking them to falling asleep faster and sleeping more deeply. Moderate activity can fit almost any time of day. Hard, sweaty workouts are usually best kept away from the last couple of hours before bed. This guide is for you if you lie awake at night, wake up unrefreshed, or want a drug-free way to sleep better, and you'd like to know which kind of movement to try first. Key takeaways Regular activity over weeks matters more than any single workout. Expect gradual change, not an overnight fix. Morning walks outdoors pair movement with daylight, which helps set your body clock. Slow, breath-focused practices such as yoga, tai chi and stretching are the best fit for evenings. Save high-intensity workouts for morning or early afternoon if late sessions keep you up. Exercise helps most sleep problems but...
Read more

Plant-Based Diet for Kidney Disease: Foods, Benefits, Meals

Image
A plant-based diet can suit many people with chronic kidney disease (CKD), and kidney organizations say eating more plants in place of red meat may help slow its progression. The catch is that potassium, phosphorus, protein and sodium still need managing, and your limits depend on your lab results. A renal dietitian should set them. This guide is for people living with CKD, and the family members who cook for them, who want to eat more plants without upsetting their blood work. Key takeaways The National Kidney Foundation says eating more plant-based foods in place of red meat may help prevent and slow the progression of chronic kidney disease. The body absorbs more phosphorus from animal foods than from plant foods, and phosphate additives in processed foods are almost completely absorbed. Foods with 200 mg or more of potassium per serving count as high-potassium, and that includes many fruits, vegetables, beans and nuts. Most adults should keep sodium to no more than 2,300 m...
Read more

Can Pinworms Last for Years? Why Infections Keep Coming Back

Image
No, a single pinworm can't live in your body for years. Adult worms live for only a few weeks. What makes an infection seem to last for months, or even years, is reinfection: eggs get swallowed again and start a new cycle before the old one ends. Break that cycle and the infection clears. This is for parents who've treated a child, seen the itching come back a few weeks later, and started to wonder whether something more serious is going on. Key takeaways Pinworms live for weeks, not years. Long-running "infections" are almost always repeated reinfections. Treatment is two doses of medicine, two weeks apart, because the medicine kills worms but not eggs. Everyone in the household needs treating at the same time, even people with no symptoms. Eggs can survive on bedding, clothes and surfaces for around two to three weeks, so cleaning matters as much as medicine. Pinworm rarely causes serious harm, but see a doctor for babies under 2, during pregnancy, or if t...
Read more

Plant Protein Powder for Acne-Prone Skin: What to Know

Image
If your skin broke out after you started whey protein shakes, switching to a plant-based protein powder is a reasonable experiment. Cow's milk has been linked with acne, and case reports describe acne flares that cleared after whey was stopped. A pea protein powder can support muscle growth, and one trial found results similar to whey. This guide is for people who lift or train and want to keep building muscle without guessing about their skin. It covers what the evidence does and doesn't show, how to choose a powder and how to run a fair test. Key takeaways The milk link is real but not fully explained: the American Academy of Dermatology (AAD) says studies link cow's milk with acne, though the reason isn't clear. Whey evidence is limited: it comes mostly from small case reports and observational studies, not large trials. Pea protein can build muscle: in a 12-week trial, pea and whey produced similar gains in muscle thickness. Sugar matters too: high-gly...
Read more

Soursop Benefits and Risks: Fruit, Leaves and Tea

Image
Soursop fruit is a healthy, fibre-rich tropical fruit that's safe to enjoy in normal amounts. Its leaves and tea have traditional uses with some early lab and animal evidence, but no human trials show soursop treats or cures cancer. High-dose leaf extracts and supplements also raise real concerns about nerve damage, so they deserve caution. This is for anyone who enjoys soursop, has been told to drink the leaf tea for a health problem, or has seen posts claiming it beats chemotherapy and wants a straight answer. Key takeaways The fruit pulp offers fibre, vitamin C and potassium, and fits well in a varied diet. Soursop extracts kill some cancer cells in lab dishes, but that hasn't been shown in people. No reputable cancer organisation supports it as a treatment. Compounds in soursop, especially concentrated in leaves, seeds and bark, can harm nerve cells. Heavy long-term use has been linked to Parkinson-like symptoms. Occasional leaf tea is different from daily concentr...
Read more

Calorie Deficit and Insomnia: Why Dieting Keeps You Awake

Image
Yes, a calorie deficit can cause insomnia. Eating less than you burn lowers overnight blood sugar, raises the hunger hormone ghrelin and nudges cortisol up, and together those signals can wake you at 2 or 3 a.m. The bigger and faster the deficit, the more likely your sleep suffers. This guide is for anyone who started a diet and suddenly sleeps worse. You'll learn how to recognize diet-related sleep trouble, and how to adjust your plan so you keep losing fat without lying awake staring at the ceiling. Key takeaways Diet-related sleep trouble usually looks like waking in the second half of the night, not trouble falling asleep. Large, fast deficits disrupt sleep more than small, steady ones. Keeping protein adequate and saving some carbohydrate for the evening often helps. Poor sleep makes dieting harder: it raises hunger and can shift weight loss away from fat and toward muscle. Loud snoring, gasping, or insomnia that started before the diet needs a medical check, not a ...
Read more

Fruits That Help Reduce Cholesterol and What to Avoid

Image
Avocado, berries, oranges and an apple, fruits that fit a cholesterol-friendly diet Fruits that are rich in soluble fiber, such as apples, pears, oranges, bananas and prunes, can help lower LDL ("bad") cholesterol as part of an overall heart-healthy diet. Avocado can help too when it replaces saturated fat. Fruit alone won't fix high cholesterol, but it's one of the easiest changes to stick with. This guide is for anyone who's just seen a high cholesterol result and wants to know what to put on the plate, and what to watch out for, especially if you take a statin. Key takeaways MedlinePlus lists apples, bananas, oranges, pears and prunes as fruit sources of soluble fiber, which helps lower cholesterol. The suggested target is 10 to 25 grams of soluble fiber a day, from fruit, oats, beans and other foods. In a small controlled study, a moderate-fat diet with one avocado a day lowered LDL more than a similar diet without avocado. Grapefruit, Seville ora...
Read more

No-Sugar Diet: How to Cut Added Sugar Step by Step

Image
A no-sugar diet means cutting added sugars, not the natural sugar in whole fruit, vegetables and plain dairy. You drop soda, sweets and sweetened snacks first, then hunt down hidden sugar in sauces, bread, yogurt and cereal. Most people get through the hardest cravings within one to two weeks. It sounds simple until you start reading labels and find sugar in pasta sauce, salad dressing and "healthy" granola. This guide is for anyone who wants to cut back without a miserable, all-or-nothing approach that collapses by week two. Key takeaways The target is added and free sugars: table sugar, syrups, honey, fruit juice and sweeteners added to processed food. The WHO advises keeping free sugars under 10% of daily calories, with extra benefit below 5%, about 25 grams or 6 teaspoons a day. The CDC reports that US adults average about 17 teaspoons of added sugar a day. Expect cravings, irritability or low energy for the first few days; they usually ease within one to two we...
Read more

Why Am I Losing Muscle Mass? Causes, Signs and Fixes

Image
Most unexplained muscle loss comes from using your muscles less, getting older, or eating too little protein and energy. Less often, it's a sign of nerve damage, a hormone problem or another illness. The good news is that the common causes respond well to regular strength training and enough protein at each meal. Maybe your legs look thinner after a few months at a desk job, or the stairs feel harder than they did last year. This guide is for anyone who has noticed that change and wants to know what's behind it and what to do next. Key takeaways Disuse is the most common cause: muscles shrink when they aren't worked regularly, and this type can often be reversed with exercise and better nutrition. Age plays a part: Cleveland Clinic says age-related muscle loss (sarcopenia) starts in your 30s or 40s and speeds up between ages 65 and 80. Strength training is the main fix: adults should do muscle-strengthening activity on at least 2 days a week, according to the CD...
Read more