The return of natural fish communities in Bohemian Forest watercourses after acidification recovery

Abstract Following decades of atmospheric acidification, the Bohemian Forest watercourses are now witnessing a remarkable resurgence of natural fish communities. This study presents the most comprehensive ichthyological survey of the region to date, covering 168 watercourse sites across the Czech and Bavarian parts of the Bohemian Forest. Using standardized electrofishing methods, we assessed species composition, density, and the presence of young-of-the-year individuals in relation to environmental characteristics. Fish were detected at 165 sites, with brown trout ( Salmo trutta ) and bullhead ( Cottus gobio ) being the dominant species. The widespread occurrence of young-of-the-year individuals indicates successful natural reproduction. Multivariate analyses revealed that fish community structure was significantly influenced by altitude, watercourse morphology, and substrate composition. Species richness increased with watercourse size and habitat heterogeneity. Acidification-sensitive species were found even in high-altitude headwaters, suggesting substantial ecosystem recovery. The near absence of invasive species further supports the high ecological quality of these watercourses. The fish fauna of the Bohemian Forest nowadays reflects the natural recovery of aquatic ecosystems after decades of atmospheric acidification. This study highlights the importance of preserving natural processes in mountain freshwater ecosystems.