Sea in which canoe collapsed? (5)
I believe the answer is:
ocean
'sea' is the definition.
(I know that sea can be written as ocean)
'canoe collapsed?' is the wordplay.
'collapsed?' indicates an anagram.
'canoe' is an anagram of 'OCEAN'.
'in which' is the link.
(Other definitions for ocean that I've seen before include "Pacific, perhaps" , "Big sea" , "It's pretty wet!" , "Great sea" , "eg Indian, Atlantic" .)