Swimmer seen among icebergs heading west (5)
I believe the answer is:
grebe
'swimmer' is the definition.
(I've seen this before)
'among icebergs heading west' is the wordplay.
'among' indicates a hidden word.
'heading west' says the letters should be written backwards.
'eberg' is hidden in the letters of 'icebergs'.
'eberg' in reverse letter order is 'GREBE'.
'seen' is the link.
(Other definitions for grebe that I've seen before include "I'll dive in" , "Flier" , "Swimmer" , "Diving bird which may be crested" , "Diver" .)