The man, who is believed to be in his fifties, was recovered from Southport Marine Lake following a call to police from a member of the public just before 09:00 BST.
Emergency services attended but the man, who has not been named, was pronounced dead at the scene.
Police said inquiries are under way to identify the man and to establish the circumstances of his death.
The body of a man has been found in a lake in Southport.