Lake bird (4)
I believe the answer is:
loon
'lake bird' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for loon that I've seen before include "Noddy" , "Fish-eating diving bird" , "Diving bird with wild cry - sounds crazy" , "Fool" , "Silly person (colloq.)" .)