Bird dog perhaps on lake (6)
I believe the answer is:
petrel
'bird' is the definition.
(petrel is a kind of bird)
'dog perhaps on lake' is the wordplay.
'dog perhaps' becomes 'pet' (dogs are often kept as pets).
'on' becomes 're' (regarding).
'lake' becomes 'L' (geographical abbreviation).
'pet'+'re'+'l'='PETREL'
(Other definitions for petrel that I've seen before include "Storm bird" , "Small seabird" , "Mother Carey's chicken" , "Seabird that flies far from land" , "Seabird sounds like fuel" .)