Disney film sees Australian following river into morass (6)
I believe the answer is:
frozen
'disney film' is the definition.
'australian following river into morass' is the wordplay.
'australian' becomes 'oz' (nickname for Australia).
'following' says to put letters next to each other.
'river' becomes 'r'.
'into' indicates putting letters inside.
'morass' becomes 'fen' (both can mean a boggy area).
'oz' after 'r' is 'roz'.
'roz' placed inside 'fen' is 'FROZEN'.
'sees' acts as a link.
(Other definitions for frozen that I've seen before include "Stiff with cold" , "Film" , "D [Disney] made" , "Ice-cold" , "Still - very cold" .)