Paddle round a river (3)
I believe the answer is:
oar
'paddle' is the definition.
(I've seen this before)
'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 "Rower's paddle" , "propels floating craft" , "Scull" , "Rowing boat operator" , "Pole for rowing" .)