Equipment for catching river fish (4)
I believe the answer is:
reel
'equipment for catching' is the definition.
(equipment for catching fish)
'river fish' is the wordplay.
'river' becomes 'r' (abbreviation for river).
'fish' becomes 'eel' (eel is a kind of fish).
'r'+'eel'='REEL'
(Other definitions for reel that I've seen before include "Dance; feel giddy" , "Lively dance; bobbin" , "Stagger around in the dance" , "Film spool" , "The angler pulls in his line using this" .)