Upon raft, travelling west across Italian river (4)
I believe the answer is:
arno
'italian river' is the definition.
(I've seen this in another clue)
'upon raft travelling west across' is the wordplay.
'across' says the answer is hidden in the clue.
'travelling west' shows that the letters should be reversed in order.
'onra' is hidden within 'upon raft'.
'onra' written backwards gives 'ARNO'.
(Other definitions for arno that I've seen before include "Banker" , "River flowing through Florence and Pisa" , "European river" , "River of 4 down?" , "River in Tuscany" .)