Cargo thrown overboard (6)
I believe the answer is:
jetsam
'cargo thrown overboard' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for jetsam that I've seen before include "Rubbish on shore thrown from ships" , "Goods thrown overboard from ship in distress" , "Unwanted material thrown overboard" , "Discarded cargo" , "Goods thrown overboard and washed up on shore" .)