Can swimming cause diarrhea? A look at recreational water illnesses

September 23, 2025 •

4 min read

According to the CDC, diarrhea is the most common illness reported in outbreaks linked to recreational water. This statistic underscores a critical question for many swimmers: can swimming cause diarrhea? The answer, unfortunately, is yes, and it’s a common health risk that every swimmer should understand to stay safe.

Quick Summary

Swallowing water contaminated with germs like Cryptosporidium, Giardia, and E. coli can cause diarrhea and other gastrointestinal illnesses. These germs can be present in pools, lakes, and oceans, even in properly chlorinated water, posing a risk to swimmers.

Key Points

Swallowing contaminated water: Accidentally swallowing water containing germs from fecal matter is the main way swimming can cause diarrhea.
Chlorine-resistant germs: Parasites like Cryptosporidium can survive for days even in properly chlorinated pools, making them a major cause of waterborne illness.
Symptoms of RWIs: Common symptoms include watery diarrhea, stomach cramps, nausea, and vomiting, often caused by parasites, bacteria (E. coli), or viruses (Norovirus).
Preventative measures: To minimize risk, shower before swimming, do not swim if you have diarrhea, and avoid swallowing the water.
Vulnerable populations: Children are at a higher risk of contracting waterborne illnesses because they are more likely to swallow water.
Natural vs. chlorinated water: While pools and lakes both pose risks, natural bodies of water can be contaminated by runoff and sewage, in addition to swimmer-borne germs.

How germs in water cause illness

Recreational water illnesses (RWIs) are caused by germs and chemicals found in water where people swim, such as pools, hot tubs, lakes, rivers, and the ocean. Diarrhea is the most commonly reported RWI. These illnesses occur when people swallow, have contact with, or breathe in mists of contaminated water. Germs can enter the water in several ways:

When they wash off swimmers’ bodies, particularly if an infected person has poor hygiene.
When a swimmer with diarrhea has a fecal incident in the water.
From sewage spills or contaminated rainwater runoff, especially in natural bodies of water.

The average adult can accidentally swallow a small amount of pool water during a swim, which can be enough to ingest these pathogens and become sick. Children are particularly vulnerable as they are more likely to accidentally swallow water while playing.

Common culprits: Parasites, bacteria, and viruses

Several types of germs are responsible for waterborne diarrheal illnesses. Understanding them is key to protecting yourself.

Parasites

Cryptosporidium (Crypto): This is the leading cause of waterborne illness in the U.S. and is notoriously resistant to chlorine. It can survive for days, even in properly treated pools. It causes watery diarrhea, stomach cramps, nausea, and vomiting.
Giardia: Another chlorine-resistant parasite, Giardia can also cause gastrointestinal symptoms like diarrhea, gas, and stomach cramps.

Bacteria

E. coli: Certain strains of E. coli can cause severe stomach cramps, bloody diarrhea, and vomiting. This bacteria is shed in the stool of infected people and animals.
Shigella: This bacterium can cause shigellosis, an infection that leads to diarrhea, fever, and abdominal pain.

Viruses

Norovirus: A highly contagious virus, Norovirus causes sudden onset of vomiting, nausea, stomach cramping, and diarrhea. It is shed in the feces and vomit of infected people and can easily contaminate water.

Preventing diarrheal illnesses while swimming

Thankfully, there are several simple yet effective steps you can take to minimize your risk of getting sick from recreational water. Adhering to these guidelines, recommended by health organizations like the CDC, benefits not only your health but the health of all other swimmers as well.

Before you get in the water:

Stay home if you are sick. Do not swim if you have diarrhea. If your child has diarrhea, keep them out of the water. For Crypto infections, it's recommended to stay out of the water for at least two weeks after symptoms stop.
Shower thoroughly. Showering with soap and water before entering the pool helps remove dirt, sweat, and other germs from your body that can deplete chlorine levels.

While in the water:

Do not swallow water. Encourage children, who are more prone to swallowing water, to avoid putting it in their mouths.
Take frequent bathroom breaks. Take children on bathroom breaks every hour and check diapers frequently away from the pool area.

Check the water:

Look for advisories. In natural bodies of water like lakes and beaches, be aware of any signs indicating pollution or harmful algal blooms, which can produce toxins that cause illness.
Verify proper maintenance. Ensure pools and hot tubs have proper water chemistry. A strong chemical smell is not an indicator of cleanliness but rather of chloramine buildup, which can irritate skin and eyes.

Understanding the risks: Chlorinated vs. natural water

The risk of illness can vary depending on the type of water body you're swimming in. While both pose risks, the types of contamination and prevention methods differ slightly.


Feature	Chlorinated Pools/Hot Tubs	Lakes/Rivers/Oceans
Primary Risk	Fecal contamination from other swimmers, especially chlorine-resistant germs like Crypto.	Contamination from sewage, animal waste, and surface runoff after heavy rain. Harmful algal blooms (HABs) can also be a factor.
Level of Control	High, assuming proper maintenance and balanced chemicals.	Low; water quality is subject to natural factors and external pollution.
Key Prevention	Swimmer hygiene (showering), avoiding swimming while sick, and checking for proper pool management.	Paying attention to public health advisories, avoiding swimming after heavy rain, and staying away from water with visible scum or algae.

For more information on water safety, consult resources from the Centers for Disease Control and Prevention (CDC Healthy Swimming).

Conclusion

It is clear that swimming can indeed cause diarrhea, primarily by ingesting water contaminated with germs. While these illnesses are common, they are also largely preventable. By practicing good hygiene, being mindful of your fellow swimmers, and avoiding the water when sick, you can significantly reduce the risk for yourself and others. Enjoy your time in the water by being informed and proactive about your health and safety.

Frequently Asked Questions

Yes, swimming in a chlorinated pool can still cause diarrhea. While chlorine kills most germs, some resilient parasites, like Cryptosporidium, are highly resistant and can survive for days, even in properly treated water.

The incubation period varies depending on the specific germ. Bacterial or viral infections may cause symptoms within a few days, while parasitic infections like Cryptosporidium can take weeks for symptoms to appear.

Yes, swallowing even a small amount of water contaminated with certain germs is enough to cause illness. For instance, a person with a diarrheal illness can release millions of germs into the water, and it only takes a tiny dose to infect someone else.

A Recreational Water Illness (RWI) is an illness caused by germs and chemicals found in water where people swim or participate in other water-related activities. Diarrhea is the most common RWI, but others can include skin rashes and ear infections.

To protect others, you should not swim while you have diarrhea. For infections like Cryptosporidium, the CDC recommends waiting at least two weeks after symptoms have completely resolved before returning to the water.

Yes, natural bodies of water like lakes and rivers can be contaminated with germs from sewage, animal waste, and surface runoff. Harmful algal blooms can also release toxins that cause diarrheal illness. Always check for public health advisories.

Teach your children not to swallow water, take them on frequent bathroom breaks, and ensure they shower with soap before swimming. If your child is sick with diarrhea, do not let them enter the water.