Between July and August, an outbreak of diarrheal illness occurred among users of a state-sponsored recreational water spraypark. Cryptosporidium hominis was isolated from the stool of some case-patients. Persons reporting water-spray exposure on their face, or in their mouths, were at increased risk for illness. Cryptosporidium hominis was detected in spraypark water and septic tank water, but not in potable or local lake water. The water for the spraypark was recycled. Filtration and disinfection procedures were inadequate to remove Cryptosporidium oocysts. It seemed likely that the spraypark water was initially contaminated by a human user.