Number 0.5: Honorable Mentions:
The Great Barrier Reef, although being 46 minutes long, it is not a movie, but instead a special episode, so Octonauts and the Great Barrier Reef does not count.
Number 1: The Octonauts and the Underwater Caves of Sac Actun
This is a movie that was released on August 5th, 2020.
The plot is an octopus friend named COBA has healed his tentacle and needs to get home to the Carribean Sea. During the test if his tentacle is ok a shark comes, and Barnacles tricks it and they get away. Peso says Barnacles isn't afraid of anything, setting up plot for later. They go by Gup H over the Ucatan Jungle but crash into birds and eventually get into a CENOTE which leads to the sea. The other octonauts have to find them, and they use a new gup, appears in SEASON 5. The GUP G. They go to the sea and eventually find a way to get in to the Cave, because Tweak and the Vegimals used the GUP M and found the cenote. Kwazii, and Dashi use the GUP Q to save Barnacle, Peso, Coba, and a new character that's Dashi's friend, RAYLA.
Number 2: The Octonauts and the Ring of Fire
It was supposed to release on October 1st, 2020, but was delayed, therefore the new release date is January 1st, 2021.
We don't know, but it will have something to do with Volcanoes and Tsunamis. It wil lalso introduce the Gup Z, based of a Mantis Shrimp. It is also called the SUPER VOLCANIC BOAT SHRIMP