Ruffle little stream after opening of fishing (5)
I believe the answer is:
frill
'ruffle' is the definition.
(I've seen this before)
'little stream after opening of fishing' is the wordplay.
'little stream' becomes 'rill' (I've seen this before).
'after' says to put letters next to each other.
'opening of' suggests taking the first letters.
The initial letter of 'fishing' is 'f'.
'rill' put after 'f' is 'FRILL'.
(Other definitions for frill that I've seen before include "Maybe superfluous piece of adornment" , "Ruff, adornment" , "Trim" , "Tuck" , "Ruche; ruff" .)