Dee Dee is a character from Dexter’s Laboratory. She wears a mermaid swimsuit in an episode "Ocean Commotion" of the show.
At the end of "Snowdown" Dee Dee tells the viewers that she remember Dexter used to have a laboratory, but Dexter and Dee Dee have got something to show the viewers, Then, when the family are at the beach, Dee Dee tries her new swimming suit, and annoys Dexter with it. Dexter pushes Dee Dee into water. Dee Dee offers Dexter her help in communicating with sealife, but Dexter dismisses her, Dee Dee then shows her ability to talk like a dolphin. Dee Dee befriends a white whale. When Dee Dee wants to stop the pirates from capturing the white whale, she is captured herself, and tied up as a ships figurehead. The white whale informs Dexter about Dee Dee's capture, and he comes to her help. The rescue ends in a giant battle and explosion. Dee Dee is freed from the ship, and while swimming, her dad catches her with his fishing-rod, at the end of "Ocean Commotion" the photographer takes a picture of Dexter's family on the Ocean Pier and in "Dexter is Dirty" Dee Dee has a bath to make it nice and clean from the mermaid.