To survive, otters need clean water in a relatively special, undisturbed environment.
That, and their small numbers over a large area, made them very vulnerable to pollution, habitat destruction and historic unregulated fishing. Unlike most people, sea otters like to cool their feet. In fact, their ice consumption is so high that Den Blå Planet has decorated the otter's enclosure with its own ice machine, so they always have a cold treat close at hand.
From the Vancouver Aquarium: Sea otters usually catch hard-shelled food - clams, abalone, clams, crabs... If they are too hard to break with their teeth, they crush them with a rock or against a rock. This is what this sea otter (Elfin) does when it hits the ice on a rock.