Seen in drink, swimmer in distress (5,2)
I believe the answer is:
shake up
'distress' is the definition.
'seen in drink swimmer' is the wordplay.
'seen in' is an insertion indicator.
'drink' becomes 'sup' (I've seen this before).
'swimmer' becomes 'hake' (I've seen this before).
'sup' going around 'hake' is 'SHAKE-UP'.
'in' acts as a link.
(Other definitions for shake up that I've seen before include "Radical reorganisation" , "Drastic reforms" , "Radical reorganization" , "Rouse" , "Jolt" .)