Fish none out from the French river (7)
I believe the answer is:
garonne
'the french river' is the definition.
(I've seen this before)
'fish none out' is the wordplay.
'fish' becomes 'gar' (gar is a kind of fish).
'out' is an anagram indicator (out can mean wrong or inaccurate).
'none' is an anagram of 'onne'.
'gar'+'onne'='GARONNE'
'from' acts as a link.
(Other definitions for garonne that I've seen before include "Toulouse's river" , "French river" , "River of Toulouse and Bordeaux" .)