Long-distance open-water swimming is a swimming discipline which takes place in outdoor bodies of water, such as open oceans, lakes and rivers. The activity has grown in popularity. This case report describes the attempt of an Olympic Champion (Maarten van der Weijden) to swim 200 km along a route taking him to eleven Frisian cities. We describe the importance of good preparation and training but also the health problems open-water swimmers, and (medical) staff, might encounter during such an extreme event. Optimal endurance, management of dizziness and hypothermia, high caloric food intake, risk of (gastrointestinal) infections and lack of sleep are all important factors to take into account in long-distance open-water swimming.