Good stroll by river getting better (7)
I believe the answer is:
gambler
'better' is the definition.
(a gambler is someone who bets)
'good stroll by river' is the wordplay.
'good' becomes 'g' (abbreviation).
'stroll' becomes 'amble' (synonyms).
'by' is a charade indicator (letters next to each other).
'river' becomes 'r' (abbreviation).
'g'+'amble'+'r'='GAMBLER'
'getting' is the link.
(Other definitions for gambler that I've seen before include "One who bets" , "One who takes risks" , "Speculator" , "Better" , "Casino punter" .)