Barney's fish on edges of water (7)
I believe the answer is:
wrangle
'barney's' is the definition.
Both the definition and answer are singular nouns.
Perhaps you can see an association between them that I can't see?
'fish on edges of water' is the wordplay.
'fish' becomes 'angle' (angle can mean to fish).
'on' is a charade indicator (letters next to each other).
'edges of' means to remove the middle letters.
'water' with its centre taken out is 'wr'.
'angle' after 'wr' is 'WRANGLE'.
Can you help me to learn more?
(Other definitions for wrangle that I've seen before include "'Quarrel, brawl (7)'" , "Angry dispute" , "Altercate" , "row" , "Haggle" .)