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…

The whales seduce each other by singing. But our heroes are there to help him compose his song. And when Barnaby and his girl end up beached, Neptuna and her friends come to their rescue once again.

The Hydronauts meet Corky, a killer whale. But Corky is not like all the others. He once lived in an amusement park and does not know how to survive on his own. Neptuna and her crew try to help him rediscover his instincts… at their own danger!

Because the ice is melting and hunting is difficult, Albert the polar bear and come to look for food on board the Hydronica. He scares the crew. But when it comes to saving a mother whale and her baby, Neptuna and the Hydronauts team up with the knowledgeable bear.

The coral are preparing for a mysterious event. All would be going well if Ponto was not having such a run of bad luck. Whatever he does, he does something stupid and upsets the coral. Neptuna and Balty try to convince him that bad luck does not exist. But above all they must correct his mistakes.

It is not only Ponto and Balty who like playing hide and seek. Some little marine animals hide under driftwood to protect themselves from predators. When Balty tries to follow their example, he hides with other fish under a piece of wood that is not drifting. The refuge becomes a trap. Will Ponto find Balty in time to help him?

The Hydronauts want to watch the right whales. But they are hiding, scared by too many gulls in the area. How can the whales and gulls be reconciled? Ask Ponto, he is a gull after all…

Dolphins live as a group so that they can better protect their young from the dangers of the sea. Not only do they protect their young, they can also come to Ponto’s rescue! But the dolphins will also need the Hydronauts’ help…

Balty is determined he has seen a ghost. On board, nobody believes him, especially not Ponto! Everybody knows there’s no such thing as ghosts! But what if Balty really did see something at the bottom of the ocean?

Ponto and Balty are fighting, they each want their own space. A bit like the crocodiles… While Neptuna helps Jonas the crocodile find a new territory, Balty meets Odile, a mother crocodile who needs his help…

The Hydronauts meet Otto, the ranger in an enormous forest of seaweed. But Otto looks after the forest on his own. It’s far too much work! Neptuna and her crew set off to find some female otters to help Otto and save the forest. But the female otters are rather demanding and difficult to please.

Ponto is sure that today Balty will meet the mammal of his life. While looking for her the Hydronauts meet many marine animals, but not a single mammal… but watch out for the tide, it’s coming in very fast and could be very dangerous!

Neptuna has lost her memory. Obo does not have a single remedy for her. A fish tells them that seahorses can cure numerous illnesses. What luck, there are seahorses living in this part of the sea. All they have to do is catch one! But what if the fish was wrong?

Balty is sure of what he has heard: Neptuna wants to return to her planet without telling them! When Ponto thinks he has seen another spaceship, he is convinced that Neptuna's friends are coming to find her! Now is the time to act. Disguised as aliens, Ponto and Balty meet manta rays and a remora fish!