Fix up a river row (7)
I believe the answer is:
arrange
'fix up' is the definition.
(synonyms)
'a river row' is the wordplay.
'river' becomes 'r' (abbreviation for river).
'row' becomes 'range' (range can mean a row or chain of things).
'a'+'r'+'range'='ARRANGE'
(Other definitions for arrange that I've seen before include "Dispose" , "Set in place" , "Put in order - organise" , "Plan, organize" , "Order, plan or design" .)