Bird fish in European river avoid (5,4)
I believe the answer is:
eider duck
'bird' is the definition.
(eider duck is a kind of bird)
'fish in european river avoid' is the wordplay.
'fish in european river' becomes 'eider' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'avoid' becomes 'duck' (ducking is a kind of avoiding).
'eider'+'duck'='EIDER DUCK'
Can you help me to learn more?
(Other definitions for eider duck that I've seen before include "Source of soft feathers" , "down supplier" , "A northern sea bird" .)