Snorkeling spot (4)
I believe the answer is:
reef
'snorkeling spot' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for reef that I've seen before include "endangered habitat" , "Coral or rock just below sea surface" , "Chain of rocks near the surface of the sea" , "Rock formed of coral" , "Submerged rocks" .)