Narrow point’s not let fluid into stream (10)
I believe the answer is:
bottleneck
'narrow point's' is the definition.
'bottleneck' can be an answer for 'narrow' (bottlenecking is a kind of narrowing). I am not sure about the 'point's' bit.
'not let fluid into stream' is the wordplay.
'fluid' is an anagram indicator.
'into' is an insertion indicator.
'stream' becomes 'beck' (northern English dialect term for 'stream').
'not'+'let'='notlet'
'notlet' anagrammed gives 'ottlen'.
'ottlen' going inside 'beck' is 'BOTTLENECK'.
Can you help me to learn more?
(Other definitions for bottleneck that I've seen before include "hold-up situation" , "Congestion" , "in which jam is concentrated?" , "Constricted place" , "tight situation" .)