Cecilia Banks is the main antagonist of the 2006 fantasy film Aquamarine. Cecilia is a beautiful and popular but spoiled, self-centered, and snobby rich girl. She is the rival of Claire, Hailey, and later Aquamarine for Raymond's affections. She is the daughter of local weatherman Storm Banks. Cecilia is portrayed by Arielle Kebbel.
After returning home form camp, Cecilia attempts to woo Raymond, much to the dismay of Hailey and Claire. Two days later, Cecilia arrives at Raymond's house as he is giving her a driving lesson. She meets Aquamarine, whom Claire claims to be her cousin, and makes fun of her. In retaliation, Aquamarine tells her that her name means dimsided and then her car blows a gasket, much to Aquamarine, Claire and Hailey's joy. After they leave, Cecilia starts to become suspicious of Aquamarine. At the fair, upon seeing Aquamarine in a hurry to get on land, she lies and tells Raymond that Aquamarine has a boyfriend, whom she is meeting to watch the sunset with. Raymond then asks Cecilia to "The Last Splash", a party held at the local beach club to celebrate the end of summer, which she accepts. The next day, however, Claire shows up at Cecilia's house and exposes her lie. To cover up the lie, Cecilia tells a friend of hers to throw Claire into the pool, but Raymond makes him put her down. After Claire leaves crying, Raymond, disgusted by Cecilia's actions and teasing, dumps her. At "The Last Splash", Cecilia attempts to confront Raymond and Aquamarine, but Hailey and Claire tell her to leave them alone. Later that night, Cecilia and her friends follow them to the water tower in her car. Although her friends want to return the party, Cecilia climbs up the water tower, and learns the truth: Aquamarine is a mermaid. Cecilia then closes the door and after she sees her friends took her car and left her, she steals and knocks down the ladder. When Cecilia returns to the beach club, she tells her friends that Aquamarine is a mermaid, but they think she has gone insane and laugh at her and walk away. The next morning, Cecilia attempts to expose Aquamarine on TV, by telling her father while she was out jogging hear noises from the water tower and believes their is a little girl trapped in there. However, Aquamarine having been saved earlier by the strange but kind-hearted beach club caretaker Leonard, the fireman finds only a blowup dolphin. After Cecilia humiliates both herself and father on TV, he severely punishes her by cutting off her driving privileges. While on the dock, when Aquamarine and Raymond are talking, Cecilia pushes her into the water, which exposes her as mermaid to Raymond. Aquamarine's father then attempts to pull her home with the tides. After Raymond leaves to help Aquamarine, Cecilia realizes that Raymond still chooses Aquamarine over her, despite Aquamarine being a mermaid, much to her fury.
- In a deleted scene, Cecilia, still angry that Raymond chose Aquamarine over her, kicks a bucket full of fish. However, she slips on water and lands into the fish, much to her horror and disgust. She then whines about how she wants her car back.