S1·E34 We've Got Fish Spirit

Oscar discovers his college dreams and aspirations are put in jeopardy because of his lack in extracurriculer activities, so Bea and Milo try to find Oscar the perfect club, and find Clamantha fighting with her arch-nemesis, Clamanda, and Milo, Oscar, and Bea's friends join Clamantha's cheerleaders team after her team gets brought by humans, but Bea turns out to be in Jumbo Shrimp and Albert Glass' map club so she is unable to help out the team.
This is a two-parter, Disney lists as episodes 133 & 134