Country river almost overwhelmed by fish (7)

I believe the answer is:

tunisia

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'country' is the definition.
(I know that Tunisia is a country)

I don't understand the rest of the clue.

(Other definitions for tunisia that I've seen before include "Suit Ian to be in North African country" , "Country which contains the site of Carthage" , "African state" , "Country in North Africa" , "Land" .)

I've seen this clue in The Times.

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