Swimmer's hairstyle (6)
I believe the answer is:
mullet
I believe this clue is a double definition.
'swimmer's' is the first definition.
(mullet is a kind of fish)
'hairstyle' is the second definition.
(I know that mullet is a hairstyle)
(Other definitions for mullet that I've seen before include "Starfish" , "Fish - bad haircut" , "Barnet?" , "Fish, male hairstyle" , "Fish (red or grey)" .)