Animal in river (5)
I believe the answer is:
hippo
'animal' is the definition.
(I've seen this before)
'in river' is the wordplay.
'in' becomes 'hip' (both can mean fashionable).
'river' becomes 'po' (Italian river).
'hip'+'po'='HIPPO'
(Other definitions for hippo that I've seen before include "Aquatic creature" , "Aquatic pachyderm" , "Aquatic mammal" , "Large semi-aquatic mammal (abbr)" , "Beastly sort" .)