Fur clad swimmer loses lead when temperature is higher (5)

I believe the answer is:

otter

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'fur' is the definition.
(otter is a kind of fur)

I don't understand how the remainder of the clue works.

(Other definitions for otter that I've seen before include "Playful aquatic animal of 'Tarka' fame" , "Semi-aquatic mammal" , "Water mammal" , "Fish eater of the weasel family" , "Lithe swimmer" .)

I've seen this clue in the Sydney Morning Herald.

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