How do otters stay buoyant in water?

Otters stay buoyant in water thanks to their dense fur and lung capacity. Their fur traps air close to their bodies, providing insulation and buoyancy. Sea otters, in particular, have the densest fur of any mammal, with up to a million hairs per square inch. They also inflate their lungs to increase buoyancy while floating on their backs. This combination of physical adaptations allows otters to remain on the water’s surface while resting, eating, or grooming.