Sweet wine container always crossing river (6)
I believe the answer is:
canary
'sweet wine' is the definition.
(sweet fortified wine)
'container always crossing river' is the wordplay.
'container' becomes 'can' (can is a kind of container).
'always' becomes 'ay' (archaic term for 'always').
'crossing' is an insertion indicator (to cross can mean to go over or around).
'river' becomes 'r' (abbreviation for river).
'ay' enclosing 'r' is 'ary'.
'can'+'ary'='CANARY'
(Other definitions for canary that I've seen before include "Bright yellow songbird" , "Bright yellow finch" , "- Wharf, - yellow" , "grass" , "A yellow singing cage-bird" .)