Dams and weirs blocking migratory fish passage affect the welfare and survival of millions of individual fish across multiple species globally.
Migratory fish that encounter impassable barriers experience individual welfare harm: they expend enormous energy attempting upstream passage, sustain physical injuries against concrete structures, and may eventually die without completing their migration. Atlantic salmon that cannot reach spawning grounds die without reproducing, representing both welfare and conservation loss. Fish ladders can mitigate but rarely eliminate passage difficulty, and poorly maintained passes are ineffective. Dam removal has been the most successful fish passage intervention, with rivers in the Pacific Northwest showing dramatic salmon recovery within years of large dam removals. The welfare and conservation cases for fish passage investment are identical.