In controlled areas, the biggest health risk you face is exposure to a parasite called Cryptosporidium parvum, commonly called crypto. This parasite causes a significant gastrointestinal illness approximately 7 days after exposure. Crypto is very resistant to normal disinfectants used in controlled pools and water parks and requires an extremely small dose to cause illness. Its normal route of transmission is through fecal oral spread and for that reason we strongly recommend all controlled pools and water parks have a written policy dealing with fecal accidents in these venues. An example of such a policy can be found at Obviously, crypto is not the only risk at controlled pools/parks, but the ability to “control” the chemical balance of the water and other environmental hazards makes it the most significant. There are many potential physical hazards such as trip and fall risks, drowning risks, and other possible bacteriological origin illness. A very informative site for more information on other swimming risks including both controlled areas and natural areas is For pool operators and those inclined to search for answers to deeper questions, we have compiled a booklet called “Swimming Pool and Spa Water Chemistry”. This booklet is excerpted from and it is an easy-to-understand guide to pool and spa maintenance and disinfection. The “Pool and Spa” home page is also a valuable resource for numerous controlled bathing area concerns.