The main focus of this study was on different case studies in the western Baltic Sea in which an insufficient hygienic bathing water quality (caused by bacterial contamination) led to bathing prohibitions or infections of bathers. A variety of model simulations were accomplished to identify the key control parameters dominating transport and occurrence of different microorganisms. It was shown that bacteria are transported with the flow which is forced by the wind itself. Additionally, supra-regional monitoring and management recommendations were derived.