Small area surrounded by water (5)
I believe the answer is:
islet
'small area surrounded by water' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for islet that I've seen before include "Little bit of land" , "Stile (anag)" , "Tiles (anag.)" , "Small landmass" , "Detached territory" .)