Crossword Genius

River mouth, a mess to some extent (6)

Ross

I believe the answer is:

thames

'river' is the definition.
(I've seen this before)

'mouth a mess to some extent' is the wordplay.
'to some extent' indicates a hidden word.
'THAMES' can be found hidden inside 'mouth a mess'.

(Other definitions for thames that I've seen before include "Sam the river" , "One going to live abroad" , "London's river (6)" , "'Old Father ___'" , "The Ma's in London" .)

I've seen this clue in The Telegraph.
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