River otters are keystone species in freshwater ecosystems whose individual welfare and population health reflect broader watershed quality, making them indicators of ecosystem welfare.
River otter welfare is intimately linked to watershed health. As apex predators in freshwater systems, otters accumulate pollutants from their fish prey, meaning water quality problems become otter welfare problems through bioaccumulation. Heavy metals, pesticides, and PCBs impair immune function, reproductive success, and neurological health in affected otters. Conversely, healthy otter populations with clean water, connected waterways, and adequate fish populations demonstrate strong welfare indicators including extensive play behavior and successful pup rearing. The recovery of river otters across their historical range represents one of conservation's success stories, but maintaining these recovered populations requires continued attention to water quality, fishing gear modification, and road crossing infrastructure to reduce mortality.