Snorkeler's sight (5)
I believe the answer is:
coral
'snorkeler's sight' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for coral that I've seen before include "Shade of pink" , "Marine polyps, often forms reefs" , "It seems like rock" , "Hard substance on the seabed" , "hard material" .)