European eels undertake one of nature's most extraordinary migrations but face near-total barriers in fragmented river systems, causing welfare harm to millions of individual fish.
River barriers cause direct welfare harm to migrating eels through exhaustion, injury, and death. Adult silver eels migrating downstream are killed or maimed by hydroelectric turbines - mortality rates of 20-50% per turbine are documented. Glass eels moving upstream expend enormous energy attempting to pass barriers, often failing and dying in the attempt. River connectivity restoration through fish passes, barrier removal, and turbine screening reduces this welfare harm while contributing to population recovery. The extraordinary life history of the European eel - born in the Sargasso Sea, living for decades in freshwater, then migrating back to breed and die - makes their welfare across this journey particularly significant.