Book associated with running water and fish (5)
I believe the answer is:
brill
'fish' is the definition.
(brill is a kind of fish)
'book associated with running water' is the wordplay.
'book' becomes 'b'.
'associated with' is a charade indicator (letters next to each other).
'running water' becomes 'rill'.
'b'+'rill'='BRILL'
'and' is the link.
(Other definitions for brill that I've seen before include "Flatfish; excellent" , "marvellous" , "catch, perhaps" , "Fab -- fish" , "Great" .)