Russian river fish -- by the smell, going out of date (11)
I believe the answer is:
obsolescent
'going out of date' is the definition.
'obsolescent' can be an answer for 'date' (thesaurus). I am not certain of the 'going out of' bit.
'russian river fish by the smell' is the wordplay.
'russian river' becomes 'Ob' (river in Russia).
'fish by' becomes 'sole' (sole is a kind of fish. I am not sure about the 'by' bit.).
'the smell' becomes 'scent' ('scent' can be a synonym of 'smell').
'ob'+'sole'+'scent'='OBSOLESCENT'
Can you help me to learn more?
(Other definitions for obsolescent that I've seen before include "Going out of use" , "on the way out" , "Outdated" , "out of fashion" , "about to disappear?" .)