Dams block fish migration routes, causing reproductive failure and population collapse for migratory species. Dam removal and fish passage infrastructure are among the highest-impact freshwater welfare interventions.
Dams impose a welfare burden on migratory fish that extends across entire river systems. Atlantic salmon, Pacific salmon, European eel, and shad evolved to complete migrations that dams now make impossible. Fish that cannot complete spawning migrations experience the physiological drive to migrate without the possibility of satisfaction — a form of chronic frustration leading to exhaustion and death without reproductive success. Beyond individual welfare, dam barriers eliminate the ecological services that migratory fish provide — nutrient transfer from ocean to river, food for terrestrial predators, and spawning gravels that support entire aquatic communities. Dam removal restores both individual fish welfare and ecosystem function simultaneously.