We conducted a pooled analysis of 13 prospective cohorts in the United States (84411 participants).7–14 We coordinated studies to ensure similar designs and measurement methods. This approach enabled us to calculate summary estimates for gastroenteritis risk and related medical and daily activity impacts associated with recreational water exposure and Enterococcus levels; it also enabled us to report for the first time,to our knowledge, separate estimates for children aged 0 to 4 and 5 to 10 years. We had 3 objectives: (1) estimate the risk of diarrhea among beachgoers associated with recreational water exposure, (2) estimate the risk of diarrhea among swimmers associated with Enterococcus levels measured in the water, and (3) estimate the illness burden attributable to recreational water exposure and exposure above regulatory guidelines for the following outcomes: diarrhea, gastrointestinal illness, missed daily activities (work, school, vacation) owing to gastrointestinal illness, and medical consultations owing to gastrointestinal illness.