Go over river with speed, travelling west (5)
I believe the answer is:
recap
'go over' is the definition.
(I've seen this before)
'river with speed travelling west' is the wordplay.
'river' becomes 'r'.
'with' means one lot of letters go next to another.
'speed' becomes 'pace' (pace is a kind of speed).
'travelling west' says the letters should be written in reverse.
'pace' reversed gives 'ecap'.
'r'+'ecap'='RECAP'
(Other definitions for recap that I've seen before include "look back on past things" , "Go over again; summarise" , "Go over study material again" , "Retrospective summary" , "Sum up (abbrev.)" .)