Duck found on European river (4)
I believe the answer is:
nile
'river' is the definition.
(Nile River is an example)
'duck found on european' is the wordplay.
'duck' becomes 'nil' (both can mean zero).
'found on' is a charade indicator (letters next to each other).
'european' becomes 'E' (abbreviation e.g. EU).
'nil'+'e'='NILE'
(Other definitions for nile that I've seen before include "eastern flower" , "Current" , "River (which is originally blue and white)" , "River of Egypt" , "Green" .)