Duck leaves lake (4)
I believe the answer is:
teal
'duck' is the definition.
(teal is a kind of duck)
'leaves lake' is the wordplay.
'leaves' becomes 'tea' (I've seen this before).
'lake' becomes 'l'.
'tea'+'l'='TEAL'
(Other definitions for teal that I've seen before include "Small river duck" , "Dark greenish-blue colour" , "Small, short-necked duck" , "Duck - dark greenish-blue" , "Variety of duck" .)