Go on a brief river excursion at the front (9)
I believe the answer is:
persevere
'go on' is the definition.
(persevering is a kind of going on)
'a brief river excursion at the front' is the wordplay.
'a' becomes 'per' (eg 'one a day' means 'one per day').
'brief river' becomes 'sever' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'at the front' says to take the initial letters.
The initial letter of 'excursion' is 'e'.
'per'+'sever'+'e'='PERSEVERE'
Can you help me to learn more?
(Other definitions for persevere that I've seen before include "Battle on" , "Fight on" , "Struggle on!" , "give it another try" , "Keep trying" .)