Dams and weirs block migratory fish from reaching spawning grounds, affecting millions of individuals and entire population welfare across river systems.
Migratory fish attempting to pass barriers face exhausting and sometimes fatal encounters with dams, weirs, and other structures. Salmon and sea trout attempt to jump barriers repeatedly, suffering physical injury and exhaustion. Those that succeed face the downstream journey for juvenile fish — passage through turbines and over spillways causes significant mortality. For individuals that cannot pass, breeding is impossible, which means the entire purpose of their migration is blocked. At the population level, barrier-induced decline in migratory fish represents a welfare problem at enormous scale — millions of fish experiencing unnecessary obstacles to fundamental life cycle behaviors. Fish passage restoration and dam removal are among the highest-impact interventions for aquatic animal welfare at landscape scale.