Go up river (4)
I believe the answer is:
burn
This clue could be a double definition.
'go up' is the first definition.
The answer and definition can be both acts as well as being singular nouns.
Perhaps there's an association between them I don't understand?
'river' is the second definition.
(thesaurus)
Can you help me to learn more?
(Other definitions for burn that I've seen before include "Scottish stream" , "Combust" , "Scottish brook" , "Scorch - stream" , "Heat injury; stream" .)