A gale affected water plants (5)
I believe the answer is:
algae
'water plants' is the definition.
(I've seen this in another clue)
'a gale affected' is the wordplay.
'affected' indicates an anagram.
'gale' is an anagram of 'lgae'.
'a'+'lgae'='ALGAE'
(Other definitions for algae that I've seen before include "Plants like seaweed" , "Stemless water plants found in a gale" , "Simple organisms, e.g. seaweeds" , "Marine growths" , "Water plants seen in a gale" .)