Try to move river to the west, but it won't fly (4)
I believe the answer is:
rhea
'fly' is the definition.
The answer and definition can be both animals as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'try to move river to the west but it won't' is the wordplay.
I cannot really understand how this works, but
'river' could be 'ea' (I've seen this in other clues) and 'ea' is found within the answer.
The remaining letters 'rh' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for rhea that I've seen before include "Titaness" , "Ostrich-like bird of South America" , "Grounded bird" , "nonflyer" , "Flightless bird - Greek fertility goddess" .)