Otters, such as this European otter, are skilful divers, capable of staying underwater for up to eight minutes. How can the marine mammals stay submerged for so long? Well, it’s all thanks to oxygen-binding proteins in their muscles that allow the animals to store reserves of oxygen in their bodies. This makes it possible for them to dive for long stretches of time without returning to the surface to breathe. While diving they also close their small ears and nostrils to prevent water rushing in. This member of the weasel family spends most of its life in the water, only stepping onto land in winter if their stretch of river freezes over. Sea otters don’t even leave the water to sleep – instead they wrap themselves in seaweed to stop themselves drifting away.