River that delivers so much! (6)

I believe the answer is:

amazon

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'river' is the definition.
(Amazon is an example)

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

(Other definitions for amazon that I've seen before include "S. America's longest river" , "World's largest river" , "woman soldier" , "Strong, aggressive woman" , "tropical fish swimming here" .)

I've seen this clue in The Guardian.

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