In August 2008, reports of an increase in cases of acute gastroenteritis (AGE) at a campground, where the drinking water supply showed abnormalities, suggested an outbreak of waterborne AGE. Environmental and epidemiological investigations were conducted to characterize the outbreak, determine its etiology and causes, and recommend appropriate control measures. An AGE outbreak was thus documented among campers at a campground during the peak tourist season. The retrospective cohort study (276 subjects) yielded an attack rate of 42%, according to the case definition proposed by the World Health Organization (WHO), and identified two transmission routes: ingestion of tap water, with a significant dose-response relationship (linear trend Chi-square p=0.00145, and an adjusted odds ratio of 3.7 for drinking 6 or more glasses of tap water per day), and swimming in the pool or river (adjusted odds ratio of 2.0 for more than one swim per day in the campground pool and/or the river). The causative pathogens could not be identified due to a lack of stool analyses and water samples collected in sufficient quantities prior to the implementation of disinfection of the water supply system. This outbreak is most likely of viral origin, given the symptoms, its duration, and the incubation period. An unreported well used by the campground owner was taken out of service. This practice indicates that water supply with insufficient pressure is likely a real problem in certain highly touristic areas. This factor should be taken into account when determining campground capacity. (R.A.)