Otter Learning To Swim

The animated Nickelodeon TV show The Penguins of Madagascar features an otter character named Marlene, voiced by Nicole Sullivan.
In the book and movie Harry Potter and the Order of the Phoenix, Hermione Granger's Patronus takes the shape of an otter.
Rigby's counterpart Doug Shlibowski from Regular Show episode "Temp Check" is an evil otter that tries to replace him as Mordecai's friend.
In "Alan Dean Foster"'s "Spellsinger" Series of Books, "Mudge the Otter" is the constant companion of the Hero of the Series Jon-Tom. Mudge is foul mouthed, lazy, greed and lecherous, he constantly derides the hero's abilities at Spellsinging, but no matter what he is loyal, courageous and funny.