Water craft seen in quantity of film about a West Country river (9)
I believe the answer is:
catamaran
'water craft' is the definition.
'catamaran' can be an answer for 'craft' (catamaran is a kind of craft). I'm unsure of the 'water' bit.
'in quantity of film about a west country river' is the wordplay.
'in' is an insertion indicator.
'quantity of film' becomes 'can' (I can't justify this - if you can you should give a lot more credence to this answer).
'about' becomes 'a' (abbreviation in Chambers).
'a west country river' becomes 'tamar' (I've seen this before).
'a'+'tamar'='atamar'
'can' enclosing 'atamar' is 'CATAMARAN'.
'seen' is the link.
Can you help me to learn more?
(Other definitions for catamaran that I've seen before include "Twin-hulled vessel" , "Boat with twin, parallel hulls" , "Twin-hulled sailing boat" , "One vessel" , "Twin- hulled vessel" .)