Close to Jenner on Russian River in the countryside (5)
I believe the answer is:
rural
'in the countryside' is the definition.
(rural means in the countryside)
'close to jenner on russian river' is the wordplay.
'close to' says to take the final letters (the close/ending of).
'on' means one lot of letters go next to another.
'russian river' becomes 'ural' (I've seen this in other clues).
The last letter of 'jenner' is 'r'.
'r'+'ural'='RURAL'
(Other definitions for rural that I've seen before include "covering the country" , "Relating to the countryside" , "Characteristic of the countryside" , "Cobbett saw on his rides?" , "Agrestic" .)