Part of the bayou sealed off from river (4)
I believe the answer is:
ouse
'river' is the definition.
(Yorkshire river)
'part of the bayou sealed off' is the wordplay.
'part of' indicates the answer is hidden within the clue.
'OUSE' is hidden in the letters of 'bayou sealed off'.
'from' acts as a link.
(Other definitions for ouse that I've seen before include "Runner" , "N English river (and S English river)" , "River flowing through York" , "Name of river in Sussex or Yorkshire" , "Lewes's river" .)