What is a recreational water illness?
The Centers for Disease Control and Prevention (CDC) defines a recreational water illness (RWI) as one that is "spread by swallowing, breathing, or having contact with contaminated water from swimming pools, spas, lakes, rivers, or oceans."
Accordingly, there's a broad range of RWIs to watch out for. The most common waterborne illnesses include E. Coli, Cryptosporidium, Giardia, Shigella, and norovirus. All of these illnesses cause diarrhea. In most cases, these diseases aren't fatal, but deaths do happen.
Less common RWIs include skin, eye, and ear infections, respiratory infections, and neurologic infections. These will manifest themselves in any number of ways: coughing, rash, fever, and more.
How do RWIs spread?
In most cases, RWIs are spread from person to person. A person infected with a diarrheal illness may have an accident while swimming, which introduces the microbe to the common area. Even if they don't, it's common for a small amount of a swimmer's fecal matter to enter the water system. When another swimmer swallows that water, he or she may also pick up the infection. This is the case no matter the body of water: pools, lakes, oceans, rivers, and so on.
Some other bacteria that cause RWIs live in the water. If a swimming pool or hot tub isn't properly sanitized, it can become a breeding ground for germs. And still waters such as lakes, and even running or tidal waters, may contain animal waste or industrial runoff or sewage. Most designated swimming spots will have been certified by a government agency as being safe for people to swim in, but not all are. Conditions may vary from one day to the next.
Swallowing germs isn't the only way to catch an RWI. Breathing vaporized, tainted water can cause respiratory illness, as can simple contact, especially in the eyes and nose. An open wound makes a swimmer particularly susceptible to infection, because it provides the germs a direct route to the bloodstream.
Children are especially vulnerable to recreational water illnesses, but pregnant women, the elderly, and people with compromised immune systems should also exercise extra caution.