Obo the computer is not working: Balty and Ponto have emptied the fresh water tanks on board the Hydronica while playing. And without Obo, the voyage cannot continue. Our friends try everything to repair him. But, there is no lack of salt water on this blue planet, fresh water is much rarer…

Balty is caught in a drift net. How can he free himself? “Wait until the net floats up to the surface” advise the fish. But Balty can’t wait that long, he’s running out of air! Let’s hope Neptuna and Ponto arrive in time to save him…

Salmon really are surprising fish! They travel up rivers to lay their eggs where they were born. They find their way by tasting the water. But the salmon are lost: the water’s taste has been changed by chemical products. Who has put detergent in the water? How can the salmon be helped? Over to Neptuna and her crew to help the salmons find their way!

Rudy the young porpoise has lost his mother. He has tried calling her, she cannot hear him over the noise of the boats. Luckily our heroes are there to help him. Especially when he has to get out of a danger zone, a shipping lane full of enormous cargo ships.

The crew of the Hydronica are confronted with an oil slick: the birds can’t fly anymore, the starfish can’t breathe… the oil must be stopped from spreading quickly. And to do it, Ponto and Balty are ready to do anything.

Our heroes meet some starving snails. They cannot find the seaweed they feed on. The natural environment appears completely disorganised. How will the Hydronauts be able to help their new friends? Balty, to Obo’s great despair, turns the Hydronica into a refuge. Neptuna, on the other hand, tries to reestablish nature’s balance.

Paul the emperor penguin needs the Hydronauts help. He is injured and cannot take care of his egg any more. A father who incubates eggs? Ponto is amazed. Yes, that’s how the emperor penguins do it! It is a difficult job for our heroes as keeping an egg warm on the ice floe is far from easy…

Sharks are terrifying animals. And Balty is not going to argue. When he and Neptuna meet Paulo, the hammerhead shark, Balty flees. But when he leaves the Hydronica, Paulo uses his very developed senses to help our friends find him. Then Ponto comes face to face with sharks. Will Balty be able to overcome his fear to save his friend?

The energy stone that makes Obo the computer work has disappeared. Neptuna and her friends must replace it so that they can continue on their voyage. They find an identical stone at Mr Octopus’s, who likes to collect shiny things to decorate his house. But Mr Octopus has no intention of helping our friends…

Leon, the cleaning fish, lives on a coral reef. Like many species, he finds what he needs to live there. But the fish have left the reef and Leon is alone, without any fish to clean and nothing to eat. Is it Jojo the biting fish’s fault? This is what our heroes will try and find out so that they can restore the natural balance on the reef.

Tamara the turtle is lost: she left to lay her eggs on the beach and has not returned to the water at nightfall. Theo, her husband, asks the Hydronauts for help. But, when they set off to find her, Neptuna and Octavia disappear too…

The Hydronica has broken down at the bottom of the ocean. How can it be fixed if nobody can go outside because of the water pressure? Especially as our friends make some disturbing discoveries in the depths of the ocean…

The manatees are very greedy animals. So when Johnny the young manatee falls ill, Neptuna and her friends think it is simply indigestions. But when all the marine animals start to fall ill, the crew start to worry. They must find out what is making the animals ill…