Duck having drink on lake (4)
I believe the answer is:
teal
'duck' is the definition.
(teal is a type of duck)
'drink on lake' is the wordplay.
'drink' becomes 'tea' (tea is a drink).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'lake' becomes 'L' (geographical abbreviation).
'tea'+'l'='TEAL'
'having' acts as a link.
(Other definitions for teal that I've seen before include "Small river duck" , "Species of duck" , "Duck; greenish-blue colour" , "Raise (subject matter)" , "Type of duck" .)