Shout for river paddle (4)
I believe the answer is:
roar
'shout' is the definition.
(roar is a kind of shout)
'river paddle' is the wordplay.
'river' becomes 'r' (abbreviation for river).
'paddle' becomes 'oar' (I've seen this in another clue).
'r'+'oar'='ROAR'
'for' is the link.
(Other definitions for roar that I've seen before include "Zoom - prolonged cry" , "Yell" , "Bellow, holler" , "Shout loudly" , "Deep-throated cry" .)