Knot perhaps for fly fisherman? (5)

I believe the answer is:

wader

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'knot perhaps' is the definition.
(I know that Calidris canutus is a type of sandpiper)

I can't explain the remainder of the clue.

Can you help me to learn more?

(Other definitions for wader that I've seen before include "crane, perhaps" , "Eg, sandpiper or plover" , "Eg, sandpiper, flamingo" , "Snipe maybe" , "Type of long-legged bird" .)

I've seen this clue in The Independent.

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