It's used for paddling round a river (3)
I believe the answer is:
oar
'it's used for paddling' is the definition.
'round a river' is the wordplay.
'round' becomes 'o' (round can mean a round object).
'river' becomes 'r'.
'o'+'a'+'r'='OAR'
(Other definitions for oar that I've seen before include "Sweep" , "Pole for rowing" , "propels floating craft" , "Bladed implement" , "Sportsman" .)