Bird plunged into water gets back (5)
I believe the answer is:
egret
'bird' is the definition.
(egret is a kind of bird)
'plunged into water gets back' is the wordplay.
'plunged into' says the answer is hidden in the clue.
'back' says the letters should be written in reverse.
'terge' is hidden within 'water gets'.
'terge' back-to-front is 'EGRET'.
(Other definitions for egret that I've seen before include "White wading bird" , "One wading" , "young bird" , "Kind of white heron - greet it" , "Heron-like wader" .)