Go off and walk in river (7)
I believe the answer is:
explode
'go off' is the definition.
(exploding is a kind of going off)
'walk in river' is the wordplay.
'walk' becomes 'plod' (plodding is a kind of walking**).
'in' is an insertion indicator.
'river' becomes 'exe' (I've seen this before).
'plod' inserted inside 'exe' is 'EXPLODE'.
'and' acts as a link.
(Other definitions for explode that I've seen before include "Go off with a bang" , "Set off" , "Detonate" , "Burst violently" , "Pop" .)