In the countryside right next to river (5)
I believe the answer is:
rural
'in the countryside' is the definition.
(I've seen this before)
'right next to river' is the wordplay.
'right next' becomes 'r' (I've seen this in other clues).
'to river' becomes 'ural' (I've seen this before**).
'r'+'ural'='RURAL'
(Other definitions for rural that I've seen before include "outside the city?" , "Countryfied" , "Countrified" , "Not urban" , "Old country fellow" .)