According to a new report from the Centers for Disease Control and Prevention's Morbidity and Mortality Weekly Report, contaminated recreational waters led to 493 reported disease outbreaks between 2000 and 2014.
These outbreaks, commonly caused by pathogens or chemicals, resulted in at least 27,219 cases and eight deaths. About half of the outbreaks started between June and August.
Public health officials examined data from 46 states and Puerto Rico for the report and found that hotel pools and hot tubs contributed to about one-third (32 percent) of the outbreaks. Public parks came in second (23 percent), then club/rec facilities (14 percent) and water parks (11 percent).
While no significant trend was observed after 2007, the CDC said outbreaks caused by the parasite Cryptosporidium, also known as crypto, increased 25 percent per year between 2000 and 2006.
Crypto can spread when people swallow something that's come into contact with an ill person's feces, such as pool water contaminated with diarrhea, according to the CDC.
"Swallowing just a mouthful of water contaminated with Crypto can make otherwise healthy people sick for up to three weeks with watery diarrhea, stomach cramps, nausea, or vomiting, and can lead to dehydration," the CDC states on its website.
Unlike Crypto, parasites Legionella and Pseudomonas can both be effectively controlled by halogens (chlorine, bromine) if the water is properly dosed. Unfortunately, 20 percent of public pools and hot tubs aren't properly dosed with disinfectant.
Legionella can lead to a pneumonia-like condition known as Legionnaire's disease or a flu-like condition called Pontiac fever. Legionella is transmitted when aerosolized water droplets often produced by hot tubs and spa jets are inhaled.
The number of outbreaks caused by Legionella increased 14 percent per year, according to the CDC report, but only accounted for 3 percent of the 363 identified microorganism outbreaks.
Pseudomonas, transmitted when skin comes in contact with contaminated water, may lead to rashes near the ear canal and otitis externa (or swimmer's ear). Pseudomonas accounted for about 4 percent of the 363 outbreaks.