Oenghus was the son of Dagda and Boann His worried parents found that his nightly visitor was a “swan woman” who  was in swan form at Lake Beal Dragan (the lake of the dragon’s Mouth).  He becomes a swan to be with her and they fly around Sid in Broige  singing and send everyone to sleep.  Like all of irish myths places in the stories actually exist.  This lake is now known as Lake Muskry in Tipperary.