Water flowing from river not well (4)
I believe the answer is:
rill
'water' is the definition.
(I know that rill is a type of channel)
'river not well' is the wordplay.
'river' becomes 'r' (abbreviation).
'not well' becomes 'ill' ('ill' is the opposite to 'well').
'r'+'ill'='RILL'
'flowing from' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for rill that I've seen before include "Flow of water" , "Burn" , "Brooklet" , "Little stream" , "Small stream" .)