Fake swamp near America (5)
I believe the answer is:
bogus
'fake' is the definition.
(I know that fake can be written as bogus)
'swamp near america' is the wordplay.
'swamp' becomes 'bog' (both can mean a wet or marshy area).
'near' says to put letters next to each other.
'america' becomes 'US' (United States).
'bog'+'us'='BOGUS'
(Other definitions for bogus that I've seen before include "Dummy" , "Mock" , "Pretended" , "Sham, counterfeit" , "Fake, phoney" .)