Argumentative type on the river? (5)
I believe the answer is:
rower
I believe this clue is a double definition.
'argumentative type' is the first definition.
(someone who gets into rows)
'on the river?' is the second definition.
(someone rowing on the river)
(Other definitions for rower that I've seen before include "Person using 9" , "crew member, perhaps" , "Perhaps stroke" , "Maybe one in eight" , "Stroke with blade" .)