Badbeard Lake is a body of water located near Clyde and Betty Jo Flynn's house, which is the home of Camp Phineas and Ferb. It is home to Spleen Island, where Badbeard buried his treasure of bad beards. Phineas, Ferb, Buford, Baljeet, Isabella, and the Fireside Girls locate this treasure in the episode "The Ballad of Badbeard". During this episode, Doofenshmirtz makes his evil lair on Spleen Island as well.
The Lake and Island are believed to be haunted by both the ghost of the pirate Badbeard, and an old sea hag. Doofenshmirtz sees a disheveled and hallucinating Candace Flynn and believes her to be the sea hag.