An outbreak of Shigella sonnei and Cryptosporidium parvum infections occurred among people exposed to an "interactive" water fountain at a beachside park in Daytona Beach, Florida. The investigation began in late August when the Volusia County Health Department (VCHD) received reports of three children with S. sonnei infection whose common exposure was play in an interactive water fountain at a beachside park that had opened August 7. To determine risk factors for gastrointestinal illness, a case-control study among a convenience sample of park attendees was performed. Among the 86 park visitors interviewed, 38 (44%) had illness that met the case definition. Onsets of illness occurred during August 15--September 2. The median age of ill persons was 8 years (range: 2--65 years); the median age of well persons was 15 years (range: 5--47 years). Twenty-five (66%) ill persons were male. The most common symptoms reported included diarrhea (97%), abdominal cramps (90%), fever (82%), vomiting (66%), and bloody diarrhea (13%). S. sonnei was isolated by culture of stool specimens from five (36%) of 14 ill persons tested. C. parvum oocysts were identified in stool specimens from two persons by light microscopy using an acid-fast stain. All 38 ill persons, compared with 32 (67%) well persons, had entered the fountain (odds ratio [OR]=undefined; 95% confidence interval [CI]=4.1--undefined). Other associated risk factors for illness included fountain water ingestion (OR=52.5; 95% CI=9.8--377.0) and consumption of food or drink at the interactive fountain (OR=4.7; 95% CI=1.6--14.3).