Idol swimming in pool (4)
I believe the answer is:
lido
'pool' is the definition.
(I've seen this before)
'idol swimming' is the wordplay.
'swimming' is an anagram indicator.
'idol' with letters rearranged gives 'LIDO'.
'in' is the link.
(Other definitions for lido that I've seen before include "---- di Jesolo, Italian Adriatic resort" , "Bathing pool" , "Open-air swimming pool" , "Public open swimming pool" , "bathing facilities" .)