Note fish out of river to the side of the boat (5)
I believe the answer is:
abeam
'river to the side of the boat' is the definition.
I can't tell whether this defines the answer.
'note fish out' is the wordplay.
'note' becomes 'a' (musical note).
'fish out' becomes 'beam' (I am not sure about this - if you are sure you should believe this answer much more).
'a'+'beam'='ABEAM'
'of' acts as a link.
Can you help me to learn more?
(Other definitions for abeam that I've seen before include "At right angles to ship's length" , "going from one side to the other" , "across width of ship" , "At right-angles to keel" , "from side to side on voyage?" .)