Angler might use this line on river (4)
I believe the answer is:
lure
'angler might use this' is the definition.
(an angler may use a lure to lure fish)
'line on river' is the wordplay.
'line' becomes 'l' (used when specifying particular lines from a poem).
'on' is a charade indicator (letters next to each other).
'river' becomes 'ure' (river in Yorkshire).
'l'+'ure'='LURE'
(Other definitions for lure that I've seen before include "Type of bait" , "Attraction" , "'Entice, tempt (4)'" , "Tempt with bait" , "Temptation" .)