Between 2012 and 2015, the collaborative research project “Sichere Ruhr” (Safe Ruhr), funded by the German Federal Ministry of Education and Research (BMBF), was conducted. It was dedicated to establishing whether the quality of Ruhr River water had improved to an extent that an existing bathing ban, issued on account of poor microbial water quality around the year 1970, could be lifted. This would meet an obvious increase in demand among a considerable proportion of the adjacent population, who already noticed the improvements in the river water quality and, in spite of the legal situation, occasionally went for a swim. Against this background and in order to investigate opportunities, perspectives and obstacles to re-opening official bathing sites along the Ruhr River, “Safe Ruhr” addressed a broad spectrum of research issues. Both microbial and parasitological pollution of the Ruhr River have been monitored extensively. Furthermore, contamination with trematodes causing “swimmers itch” has been evaluated. The main sources for microbial pollution in the river were identified as being combined sewer overflows (CSOs), sewage water treatment effluents and agricultural runoff. Models to assess the variable impact of these pathogen pathways as well as early warning systems for hygienic quality have been developed and evaluated. Microbial health impacts and the health risk of river bathing have been assessed by use of quantitative microbial risk assessment (QMRA) and the concept of disability-adjusted life years (DALY). Different technologies to reduce pathogens in CSO effluents have been implemented and tested. In order to facilitate the re-establishment of Ruhr River bathing sites, a cost-benefit analysis for bathing in the Ruhr River was performed, a regional stakeholder analysis has been conducted, a communication strategy has been developed and a comprehensive practical guideline for bathing in natural watercourses has been published.