Wreck in American harbour (6)
I believe the answer is:
marina
'harbour' is the definition.
(marina is a type of harbour)
'wreck in american' is the wordplay.
'wreck' becomes 'mar' (I've seen this in another clue).
'american' becomes 'a' (common abbreviation - e.g. in organisation names).
'mar'+'in'+'a'='MARINA'
(Other definitions for marina that I've seen before include "place to moor up?" , "Dock for pleasure craft" , "boating facility" , "Yacht harbour" , "Place for mooring boats" .)