Exposure to splash water and to water from the drinking fountain at an Idaho water park were associated with an outbreak of Cryptosporidiosis. Duration of splash water exposure was positively associated with illness. Laboratory samples collected from the splash fountain, filter backwash, and drinking fountain water showed the presence of Cryptosporidium. Two case-patients and each environmental isolate were genotyped Cryptosporidia hominis laA28R4, which is predominantly a human pathogen. Diapered children were observed to be using the splash fountains so there was a possibility that human fecal contamination of the water could have occurred.