Fish ladders and bypass channels are engineering solutions designed to allow migratory fish to pass dams and weirs, but their effectiveness varies enormously and has direct implications for fish welfare and population health.
Fish ladders address a genuine welfare problem: dams fragment river systems and prevent migratory fish from completing life cycle journeys that are fundamental to their biology. Fish unable to migrate to spawning grounds experience reproductive failure and prolonged physiological stress from disrupted hormonal cycles. The welfare impact extends beyond individual animals to population-level collapse. However, poorly designed passage infrastructure can create welfare traps where fish repeatedly attempt and fail passage at enormous energetic cost. Investment in fish passage design quality and, where feasible, dam removal rather than ladder retrofitting, delivers the greatest welfare returns.