Most of the time when beaches are closed or advisories are issued, it's because the water has high levels of harmful microorganisms (or microbes) that come from untreated or partially treated sewage: bacteria, viruses, or parasites. We also use the word "pathogens" when they can cause disease in humans, animals, and plants.
Children, the elderly, and people with weakened immune systems are most likely to develop illnesses or infections after coming into contact with polluted water, usually while swimming. The most common illness is gastroenteritis, an inflammation of the stomach and the intestines that can cause symptoms like vomiting, headaches, and fever. Other minor illnesses include ear, eye, nose, and throat infections
Fortunately, while swimming-related illnesses are unpleasant, they are usually not very serious - they require little or no treatment or get better quickly upon treatment, and they have no long-term health effects. In very polluted water, however, swimmers can sometimes be exposed to more serious diseases like dysentery, hepatitis, cholera, and typhoid fever.
Most swimmers are exposed to waterborne pathogens when they swallow the water. People can get some infections simply from getting polluted water on their skin or in their eyes. In rare cases, swimmers can develop illnesses or infections if an open wound is exposed to polluted water.
Not all illnesses from a day at the beach are from swimming. Food poisoning from improperly refrigerated picnic lunches may also have some of the same symptoms as swimming-related illnesses, including stomachache, nausea, vomiting, and diarrhea.
It is also possible that people may come into contact with harmful chemicals in beach waters during or after major storms, especially if they swim near what we call “outfalls,” where sewer lines drain into the water. You can learn more about this by visiting our web site for stormwater.
Finally, the sun can hurt you if you're not careful. Overexposure can cause sunburn, and over time, it can lead to more serious problems like skin cancer. The sun can also dehydrate you and cause heat-related illnesses like heat exhaustion, muscle cramps, and heat stroke. Learn more about sun safety at our SunWise site or heat-related illnesses at the Centers for Disease Control and Prevention site.
How to Stay Safe
There are several things you can do to reduce the likelihood of getting sick from swimming at the beach. First, you should find out if the beach you want to go to is monitored regularly and posted for closures or swimming advisories. You are less likely to be exposed to polluted water at beaches that are monitored regularly and posted for health hazards.
In areas that are not monitored regularly, choose swimming sites in less developed areas with good water circulation, such as beaches at the ocean. If possible, avoid swimming at beaches where you can see discharge pipes or at urban beaches after a heavy rainfall.
To find out about the beaches you want to visit, contact the local beach manager.
Since most swimmers are exposed to pathogens by swallowing the water, you will be less likely to get sick if you wade or swim without putting your head under water.