Hounds romping in North American river (6)

I believe the answer is:

hudson

I'm a little stuck... Click here to teach me more about this clue!

'north american river' is the definition.
(I've seen this in another clue)

'hounds romping' is the wordplay.
'hounds' can be anagrammed to 'HUDSON'.
However, I'm not sure how the anagram is indicated.

'in' is the link.

Can you help me to learn more?

(Other definitions for hudson that I've seen before include "Major inland sea of NE Canada - . . . . . . Bay" , "Rock --, US actor" , "8 [BUTLER" , "ROCK] a > banker" , "New York river; Upstairs/ Downstairs butler" .)

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