Peso and the gang try to repair a reef by replacing bleached corals, but a pod of playful dolphins make mischief for them until they discover that helping can be fun too.

Gup-G - a Gup based on a salamander. It appears in the episode The Yangtze River The Chinese giant salamander episode. More on that here. It will appear in Season 5. It has early screenings in Octonauts and The Caves of Sac Actun. It has retractable legs that expand to help it stand and walk on land and contract to move fast through the water. The mouth can open up and act as a way to enter or exit the ocean or land. It is able to fit everyone inside. Using its mouth, it can also release certain Gups.Shellington and the others round up some lost crabs and marine iguanas that have got marooned on an island far too cold for them and take them home to the Galápagos Islands.

Hungry gulper eel brothers as well as undersea tremors threaten Inkling and Kwazii and get trapped by boulders. So Dashi uses Tweak's newly built "Octo Mach-Suit" to rescue them. In The Hammerhead Sharks, the Gup is mistaken for a stingray and the Shark Pup Siblings try to eat it. In March 2023, five new episodes under the original Octonauts branding and format were released via the BBC iPlayer. The Octonauts venture inside a whale shark again (see Series 1, episode 1), this time they need to rescue a porcupine puffer fish named Puffy before it's too late! a tiger shark camouflage mode to scare away other predators (since tiger sharks can eat almost anything).

When an underwater hurricane destroys a small reef, which a frogfish and other creatures depend on, Tweak and her crew must convert the recently destroyed Gup-F into an artificial reef before the second stage of the hurricane strikes!