Atlantic salmon populations have collapsed across UK and European rivers due to barriers, water quality degradation and marine survival problems, with individual fish welfare closely tied to river conditions.
Salmon migrating through degraded rivers face oxygen depletion in warm, polluted water causing physiological stress and mortality. Barriers force fish to attempt exhausting jumps repeatedly. Fish in crowded migration bottlenecks face territorial aggression. The welfare of individual salmon is compromised throughout the migratory journey in most UK rivers.