Dredger expected river to be full of stone (6)
I believe the answer is:
duster
'dredger' is the definition.
'expected river to be full of stone' is the wordplay.
'expected' becomes 'due' (I've seen this before).
'river' becomes 'r'.
'to be full of' indicates putting letters inside.
'stone' becomes 'st'.
'due'+'r'='duer'
'duer' placed around 'st' is 'DUSTER'.
(Other definitions for duster that I've seen before include "Polishing cloth" , "Cloth for removing surface powder" , "cleaner" , "yellow cloth" , "Soft cloth for cleaning surface" .)