Watergate is involved with the clue (6)
I believe the answer is:
sluice
'watergate' is the definition.
(I've seen this before)
'is involved with the clue' is the wordplay.
'involved with' indicates anagramming the letters (involved can mean confusing or complex).
'is' anagrammed with 'clue' gives 'SLUICE'.
(Other definitions for sluice that I've seen before include "really wet" , "Sliding gate to control water in stream" , "Water drainage channel" , "Flush" , "Floodgate" .)