Rupert's Undersea Adventure is the 10th episode of Rupert (TV series) and the 10th episode of season 1.
When Rupert is falsely accused, caught and tried by King Neptune's undersea court for kidnapping his prized Whistle Fish, it's up to Rupert and a little mermaid, Marina, to race against time and save the Fish, demonstrating that creatures of the land and sea must work together for the benefit of all.
- At the start of the episode when Rupert walks down the beach, he is whistling his theme song from the series. The whistlefish starts to whistle the tune with him. This is the first time he whistle his theme song, the second time is in the episode Rupert and Growler.
- It's the first time that the titlecard uses a extra 's in the logo of the series to name a episode.
- This is the first time in the series that Rupert visits Rocky Bay