Otters need clean water, abundant prey (fish, crustaceans, molluscs), and dense bankside cover for holts. Pollution and habitat fragmentation are the principal threats.
Most species are tightly tied to clean rivers, lakes, and wetlands. Indicator-species status: an otter population implies a functioning aquatic ecosystem.
Sea otters favour kelp-forest coastlines with shallow rocky reefs and urchin populations. They rarely come ashore.
Otters occupy every continent except Australia and Antarctica. Densest populations remain in the Amazon, Congo basin, and Pacific Northwest.