River creature upset concerning fluid flow (7)
I believe the answer is:
laminar
'flow' is the definition.
(laminar flow is a kind of flow)
'river creature upset concerning fluid' is the wordplay.
I cannot really understand how this works, but
'river' could be 'r' (abbreviation for river) and 'r' is present in the answer.
'fluid' could be 'n' (N is an example) and 'n' is located in the answer.
The remaining letters 'lamia' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for laminar that I've seen before include "Running in flat layers" , "Made of thin layers" , "sheet upon sheet" , "Like streamlined flow" , "Like some thin plates" .)