Flowing water about to invade street in the morning (6)
I believe the answer is:
stream
'flowing water' is the definition.
(I've seen this before)
'about to invade street in the morning' is the wordplay.
'about to' becomes 're' (I've seen this in other clues).
'invade' is an insertion indicator.
'street' becomes 'st'.
'in the morning' becomes 'am'.
'st'+'am'='stam'
're' going inside 'stam' is 'STREAM'.
(Other definitions for stream that I've seen before include "Transmit music or video online" , "Master (anag) - current" , "divide pupils into ability groups" , "Brook or small river" , "Fly" .)