River rising fast is evocative (8)
I believe the answer is:
redolent
'is evocative' is the definition.
(synonyms)
'river rising fast' is the wordplay.
'river' becomes 'oder' (River Oder in central Europe).
'rising' says the letters should be written in reverse (going up in a down clue).
'fast' becomes 'lent' (Lent is a period of fasting in Christianity).
'oder' back-to-front is 'redo'.
'redo'+'lent'='REDOLENT'
(Other definitions for redolent that I've seen before include "Strongly reminiscent (of something)" , "Smelling strongly or suggestive of it" , "Aromatic" , "odorous" , "Strongly suggesting" .)