Tens of thousands of obsolete dams, weirs, and culverts block wild salmon migration in European rivers, causing population collapses that represent both a conservation crisis and an enormous individual welfare cost.
Wild salmon attempting to migrate past impassable barriers experience repeated failed attempts, energy depletion, and ultimately reproductive failure. Fish that cannot reach spawning grounds die without reproducing, representing both an individual welfare loss and population-level harm. In rivers where partial passage is possible, barriers create bottlenecks where fish accumulate, increasing predation pressure and disease transmission. The removal of even small, obsolete barriers can rapidly restore salmon passage to tens of kilometres of upstream habitat, representing one of the highest-return interventions for both welfare and conservation.