Blooming angry expression during riparian activity (11)
I believe the answer is:
flourishing
'blooming' is the definition.
(thesaurus)
'angry expression during riparian activity' is the wordplay.
I cannot quite see how this works, but
'during' could be 'in' (e.g. during February means in February) and 'in' is found within the answer.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for flourishing that I've seen before include "Waving around" , "Prospering - showing off" .)