Feathered, they skim the water (4)
I believe the answer is:
oars
'feathered they' is the definition.
The definition suggests a plural noun which matches the answer.
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for oars that I've seen before include "Implements of propulsion on water" , "Propellers for small boat" , "These could make you row" , "Implements to propel a boat" , "Boating implements" .)