Look! Identification dropped in pool (4)
I believe the answer is:
lido
'pool' is the definition.
(I've seen this before)
'look identification dropped in' is the wordplay.
'look' becomes 'lo'.
'identification' becomes 'id'.
'dropped in' means one lot of letters goes inside another.
'lo' going around 'id' is 'LIDO'.
(Other definitions for lido that I've seen before include "---- di Jesolo, Italian Adriatic resort" , "Swimming and leisure area" , "Aquatic leisure centre" , "Venice's beach island facing the Adriatic" , "Venetian resort" .)