Nasty smell from river — no good (4)
I believe the answer is:
pong
'nasty smell' is the definition.
(pong can informally mean a bad smell)
'river no good' is the wordplay.
'river' becomes 'Po' (Italian river).
'no good' becomes 'ng' (abbreviation).
'po'+'ng'='PONG'
'from' is the link.
(Other definitions for pong that I've seen before include "Ping's regular partner?" , "In slang, a real stink" , "hum" , "Bad smell" , "Smell unpleasantly" .)