One who fishes in corner by river (6)
I believe the answer is:
angler
'one who fishes' is the definition.
'corner by river' is the wordplay.
'corner' becomes 'angle' (I've seen this before).
'by' is a charade indicator (letters next to each other).
'river' becomes 'r'.
'angle'+'r'='ANGLER'
'in' is the link.
(Other definitions for angler that I've seen before include "Sportsman" , "Fisher with hook and line." , "who looks for compliments" , "A rod-and-line fisherman" , "One hoping for a catch" .)