Whitewater conveyance (4)
I believe the answer is:
raft
'whitewater conveyance' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for raft that I've seen before include "Flat floating device" , "Floating log structure; large amount" , "Travel on river, in a way" , "Flat floating structure used as boat" , "A whole lot" .)