Water mammal
I believe the answer is:
otter
'water mammal' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for otter that I've seen before include "Torte (anag)" , "Semi-aquatic creature" , "Water animal with webbed fee, brown fur and flat tail" , "one that eats fish" , "Aquatic river mammal" .)