Watercourse given protective coating and made more efficient (11)
I believe the answer is:
streamlined
'made more efficient' is the definition.
(I've seen this before)
'watercourse given protective coating' is the wordplay.
'watercourse' becomes 'stream' (synonyms).
'given protective coating' becomes 'lined' (I can't justify this - if you can you should believe this answer much more).
'stream'+'lined'='STREAMLINED'
'and' is the link.
Can you help me to learn more?
(Other definitions for streamlined that I've seen before include "Of sleek appearance" , "Designed to reduce wind resistance" , "made more efficient" , "Shaped for speed" , "Designed for smooth flow" .)