Duck finding meal on lake (4)
I believe the answer is:
teal
'duck' is the definition.
(teal is a type of duck)
'meal on lake' is the wordplay.
'meal' becomes 'tea' (tea is a type of meal).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'lake' becomes 'L' (geographical abbreviation).
'tea'+'l'='TEAL'
'finding' acts as a link.
(Other definitions for teal that I've seen before include "bird" , "Strange tale of a duck" , "Species of duck" , "Small freshwater duck and colour" , "Variety of duck" .)