It grows down river in Germany (5)
I believe the answer is:
eider
I believe this is a double definition.
'it grows down' is the first definition.
(eider ducks grow down feathers)
'river in germany' is the second definition.
(Eider is a German river)
(Other definitions for eider that I've seen before include "Northern sea duck" , "Source of fine soft down" , "Duck noted for down" , "Duck from which down is obtained" , "Duck supplying down" .)