Notebook Jack’s lost depicting furry swimmer (5)
I believe the answer is:
otter
'furry swimmer' is the definition.
(I've seen this in another clue)
'notebook jack's lost' is the wordplay.
'notebook' becomes 'jotter' (jotter is a kind of notebook).
'jack' becomes 'J' (playing card abbreviation).
'lost' is a deletion indicator.
'jotter' with 'j' removed is 'OTTER'.
'depicting' acts as a link.
(Other definitions for otter that I've seen before include "Water animal with webbed fee, brown fur and flat tail" , "Freshwater carnivorous mammal with webbed and clawed feet" , "Mammal, 'Tarka'" , "Aquatic river mammal" , "Riverine mammal" .)