Spook just haunting wetland (8)
I believe the answer is:
frighten
'spook' is the definition.
(I know that spook is a more specific form of frighten)
'just haunting wetland' is the wordplay.
'just' becomes 'right' (associated in meaning).
'haunting' indicates putting letters inside (haunt can mean to visit).
'wetland' becomes 'fen' (I've seen this in another clue).
'right' put within 'fen' is 'FRIGHTEN'.
(Other definitions for frighten that I've seen before include "Cause alarm" , "Shock" , "Terrify" , "Cause fear" , "Cow" .)