Fare to get across lake or swamp (5)
I believe the answer is:
flood
'swamp' is the definition.
(synonyms)
'fare to get across lake' is the wordplay.
'fare' becomes 'food' (fare can mean food).
'to get across' indicates putting letters inside.
'lake' becomes 'l' (geographical abbreviation).
'food' enclosing 'l' is 'FLOOD'.
'or' acts as a link.
(Other definitions for flood that I've seen before include "Light" , "Spate" , "swamp" , "lot of water" , "Overwhelming amount" .)