Duck problem raised in lake report's preface (9)

I believe the answer is:

merganser

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'duck' is the definition.
(I know that merganser is a type of sea duck)

I cannot understand how the remainder of the clue works.

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

I've seen this clue in The Daily Express.

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