Get up river on river (5)
I believe the answer is:
rouse
'get up' is the definition.
(thesaurus)
'river on river' is the wordplay.
'river' becomes 'r'.
'on' is a charade indicator (letters next to each other).
'river' becomes 'ouse' (Yorkshire river**).
'r'+'ouse'='ROUSE'
(Other definitions for rouse that I've seen before include "Cause to wake up and come alert" , "Disturb" , "Activate, wake up" , "Stir from inactivity" , "cause to wake or to become active" .)