To sprinkle with sugar is a drag (6)
I believe the answer is:
dredge
I believe this is a double definition.
'to sprinkle with sugar' is the first definition.
(sprinkle food with powder like sugar or flour)
'a drag' is the second definition.
(clear bed of body of water)
'is' acts as a link.
(Other definitions for dredge that I've seen before include "Search" , "Clear a channel" , "Dig up mud from river or canal bed" , "Clean mud as from silted harbour" , "Sprinkle flour" .)