Appearance of water restricting river's flow (6)
I believe the answer is:
stream
This clue might be a double definition.
'appearance of water' is the first definition.
'stream' can be an answer for 'water' (stream is a kind of water). I'm not sure about the 'appearance of' bit.
'restricting river's flow' is the second definition.
'stream' can be an answer for 'flow' (synonyms). I'm not certain of the 'restricting river's' bit.
Can you help me to learn more?
(Other definitions for stream that I've seen before include "Quantity of water" , "One small river" , "River - current" , "Flow from master" , "comprising a load of drips?" .)