Animal in water, a turtle (3)
I believe the answer is:
rat
'animal' is the definition.
(rat is a kind of animal)
'in water a turtle' is the wordplay.
'in' indicates the answer is hidden within the clue.
'RAT' is hidden in the letters of 'water a turtle'.
(Other definitions for rat that I've seen before include "Rodent - deserter" , "Grass" , "that gets out of stricken vessel" , "Scumbag" , "Destructive rodent" .)