How dam constructors work hard? (6)

I believe the answer is:

beaver

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'work hard?' is the definition.
(I've seen this before)

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

(Other definitions for beaver that I've seen before include "Work hard" , "Small animal that builds dams on rivers" , "Rodent - fur - hat - glove - cloth - junior Scout" , "Amphibious animal, lives in lodge" , "Furry animal, lives in lodge and builds dams" .)

I've seen this clue in The Sun and The Times.

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