Extreme Heat Threatens Fish Populations in German Rivers

Extreme heat and prolonged drought are worsening the plight of fish in Germany's rivers, with emergency rescues underway in critical areas. Rising temperatures, falling water levels, and oxygen depletion are pushing aquatic species to the limit, particularly in former branches of the Danube near Straubing, Bavaria, as well as in canals and tributaries in Freiburg, North Rhine-Westphalia, and Rhineland-Palatinate. ## Danube Branches Under Extreme Stress The most severe conditions are found in the Danube's dead branches-isolated sections that serve as vital refuges and spawning grounds. Many fish arrived there in spring to reproduce, but now find themselves trapped as water levels drop. Stefan Plendl, president of the Straubing fishing club, described the dire situation, noting that surface temperatures of 34°C are heating the water to dangerous levels. "At these temperatures, oxygen levels become critically low," Plendl explained. "When oxygen saturation falls below 30%, it becomes fatal for predatory fish and whitefish." In some areas, oxygen levels have dropped to just 30-32%, threatening entire populations. Plendl warned that if the heat persists and water levels continue to fall, the ecological consequences could be catastrophic, with years of reproduction at risk. ## Emergency Rescues in Critical Zones In Pillmoos/Zeller Wörth, near Straubing, fishermen and water management authorities are pumping water from the Danube into a dying branch to prevent mass fish deaths. The operation, which requires 80-100 liters of diesel per day, is a stopgap measure to sustain a key spawning area. However, in Vogelau, the drought has advanced so far that pumping is no longer feasible, forcing rescuers to manually relocate fish to safer waters. Similar efforts are underway in Freiburg, where a sports fishing club is rescuing fish from nearly dry canals. In some areas, water levels have dropped to just 5-6 centimeters, leaving thousands of fish stranded. The crisis extends beyond fish, with endangered species like the crested newt also at risk. In Straubing’s Gstütt Island, fishermen collected hundreds of these vulnerable amphibians by hand. ## Broader Ecological Impact The drought is not only affecting fish but also crab, mussel, and tadpole populations. Dead branches of rivers play a crucial role in supporting biodiversity, serving as habitats for amphibians, birds, and other aquatic organisms. When these areas dry up or lose oxygen, the entire riverine ecosystem suffers. Plendl criticized the Danube’s modernization for failing to adequately protect these side habitats, compounding the damage. The crisis has also spread to other regions, with North Rhine-Westphalia’s Environment Ministry warning of severe impacts on trout and grayling populations. In Rhineland-Palatinate, small streams and tributaries of the Rhine, Moselle, Lahn, and Nahe are drying up, leaving only isolated pools with dangerously low oxygen levels.