Fishing bait left next to river (4)
I believe the answer is:
lure
'fishing bait' is the definition.
(type of bait in fishing)
'left next to river' is the wordplay.
'left' becomes 'l' (common abbreviation).
'next to' is a charade indicator (letters next to each other).
'river' becomes 'ure' (I have seen 'River of Wensleydale ' mean 'ure' so perhaps 'river' could also mean 'ure').
'l'+'ure'='LURE'
(Other definitions for lure that I've seen before include "Type of bait" , "Tempt with bait" , "Temptation" , "Attract with bait" , "draw" .)