Hydroelectric dams block migratory fish routes and cause significant individual welfare harm through energy expenditure at barriers, turbine passage trauma and the loss of spawning access for species that evolved long-distance migrations.
Dam impacts on migratory fish welfare extend from the individual scale — fish struggling exhaustingly at impassable barriers, suffering turbine injuries, or dying before reaching spawning grounds — to the population scale of species whose entire lifecycle depends on migration routes now blocked. Fish repeatedly attempting passage at barriers experience physiological exhaustion equivalent to sustained extreme exercise. Turbine passage injuries cause hemorrhage, organ damage and scale loss that may be non-lethal but cause prolonged welfare harm in survivors. Fish unable to reach natal spawning grounds cannot complete their reproductive destiny — a frustration of fundamental behavioral drives that may constitute a welfare harm even if the neurological substrate is uncertain. Dam removal is the most effective intervention and has proven its value in restoring populations rapidly.