Swimmer deploying green arms (9)

I believe the answer is:

merganser

'swimmer' is the definition.

'deploying green arms' is the wordplay.
'deploying' is an anagram indicator.
'green'+'arms'='greenarms'
'greenarms' is an anagram of 'MERGANSER'.

(Other definitions for merganser that I've seen before include "Together saw bill" , "Diving duck" , "Sawbill" , "Diver" , "Diving bird" .)

I've seen this clue in The Guardian.

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