Five epidemiological studies were performed following a randomised, controlled study design in order to evaluate the risk of contracting infectious diseases from bathing in fresh water. Study locations were situated in the north, east, southwest and southeast of Germany: four sites on lakes and one site on a river. All sites had complied with current EU regulations for at least the three previous years. The sources of faecal contamination included raw and treated municipal sewage, agricultural and municipal run-off after rainfall and contamination by water fowl.