At the river, fish and swim (4)
I believe the answer is:
reel
'swim' is the definition.
(I've seen this before)
'at the river fish' is the wordplay.
'at' is a charade indicator (letters next to each other).
'the river' becomes 'r' (abbreviation for river).
'fish' becomes 'eel' (eel is a kind of fish).
'r'+'eel' is 'REEL'.
'and' acts as a link.
(Other definitions for reel that I've seen before include "Part of film; dance" , "Stagger with rod winder" , "Move unsteadily (like a Scottish dancer?)" , "Photographer's and anglers spool" , "Dance - bobbin - stagger" .)