Unusually silent creeks (6)
I believe the answer is:
'creeks' is the definition.
(I've seen this in another clue)
'unusually silent' is the wordplay.
'unusually' indicates anagramming the letters.
'silent' anagrammed gives 'INLETS'.
(Other definitions for inlets that I've seen before include "Silent sort of sea strips" , "Silent strips of water" , "Sounds" , "Silent kind of water channels" , "Bays or coves" .)