The Hidden Lake
Season 04, Episode 02
The Hidden Lake
Episode guide
The Poison Dart Frogs
The Octopod Mystery


The Hidden Lake is Season 4 Episode 2 of the Octonauts series. The Octonauts explore Antarctica in the Gup-S. They manage to discover a legendary mystery. A hidden lake which has been sealed by the ice for millions of years. It appears that the water is red because of all the rust in the water, which contains heaps of iron. In this episode the Gup S' drill actually breaks while trying to burrow into the ice. Upon reaching the lake, initially there doesn't seem to be any living creatures so Shellington takes a water sample to study in the Gup-S. It so happens that he hears a voice, which appears to be a microbe named Meryvn! As he can't stand the heat of the Gup-S, Shellington scrambles back to the hidden lake so that the microbe can survive.

Creature Reports



Colour in the Antarctic

Shellington wishes to find out if there are any creatures living above the Antarctic ice, so he, Captain Barnacles, Kwazii and Peso prepare to start exploring in the Gup-S. It seems like there are no creatures around, but Kwazii suddenly notices what appears to be a red frozen waterfall. Intrigued, the Octonauts decide to get a closer look and activate the Ice-Spy. It shows them that there is a red lake underneath the ice and so they start to use the GUP-S' drill to break through it. This unfortunately leads to the drill breaking, but they still manage to make it through the ice. Barnacles decides that exploring the lake is more important than immediately repairing the drill, but to his surprise, Shellington has long exited the GUP, clearly eager to get started. Kwazii is impressed by this.

Inside the red lake

Now in the water, Shellington reveals to the group that it has turned red because of two things: rusted iron particles and excessive salt. Kwazii and Peso remark that the water is also very cold and dark, so Shellington decides that nothing could possibly survive in it. Captain Barnacles tells him that they'd better be going, but he takes a water sample first.

Back in the GUP

Shellington is unhappy that he did not discover any new creature, so the other Octonauts try to cheer him up by speaking positively about the situation. Captain Barnacles then says that they should rest in the GUP before returning home. Kwazii tells him that it's still light outside, but Barnacles reminds him that in the Antarctic, it doesn't get dark at that time of year. Kwazii says he will have trouble sleeping due to this, but cleverly rectifies the situation by wearing two eyepatches instead of one.

The microbe

Barnacles, Kwazii and Peso are asleep, but Shellington is still awake, organising his water samples. He suddenly hears a voice, and thinks he is hearing things so tries to also go to sleep. But when the voice calls again, he looks inside his water sample through a microscope, and sees a living creature inside! It introduces itself as Mervyn, a microbe who cannot be seen without a microscope. After a chat, Mervyn begins to feel unwell, and indistinctly reveals that he is unable to survive outside of the red lake. Shellington quickly goes back to the ice hole so he can return Mervyn to his home.

Back in the red lake, Mervyn happily introduces Shellington to his friends, three other microbes named Jeb, Shirley and Alice. They reveal that they do not eat food but simply gather energy from the rust in the water. After learning something new about microbes, Shellington suddenly begins to see a problem with being in the lake: he does not know the way out! To make matters worse, the light on his deep-sea suit freezes and stops working. Beginning to panic, he tries to send a distress call to the GUP-S, which happens to wake up Kwazii. He falls off his bed, and the noise wakes Captain Barnacles who is then able to hear the distress call. Kwazii, bumping into things due to the eyepatches, causes Captain Barnacles to accidentally sound the Octo-Alert.

The rescue

Barnacles, Kwazii and Peso gather by the ice hole. As the GUP-S' drill broke earlier, Shellington would be permanently stranded should the hole freeze over. Barnacles and Kwazii make it into the lake, but cannot see him anywhere. They begin to hear some voices calling their names, and decide to follow them. The voices eventually lead them straight to Shellington, and it is revealed that the microbes showed them the way. The others are introduced, but Peso suddenly alerts them via radio that the ice hole is freezing over, and they should hurry. Shellington promises to come and visit them another time, and they wave goodbye. They quickly climb back up the hole, and Peso lowers the GUP-S' towline to them. He then accidentally sets the GUP into turbo mode, and while this successfully pulls them out, it also causes chaos. The three fall into a pile of snow as a result, and Captain Barnacles compliments Peso on his "nice driving".

As the Octonauts drive home, they talk about the unusual creatures they discovered. Peso, having not seen them, asks Shellington how many microbes he thinks there were altogether. His answer is "about 10,003,062".


  • Dashi, Tweak, Professor Inkling, Tunip and the Vegimals do not appear in this episode, making it the Octonauts episode which features the fewest characters. Counting the discovered microbes, only seven characters appear throughout the episode.
  • This is the first time Tweak and Dashi have been absent in an episode (although they have both had occasional non-speaking roles in earlier episodes), but Professor Inkling and the Vegimals were also completely absent in episode 3, The Crab and Urchin.
  • Also, although it is indirectly mentioned, it is the first episode not to feature the Octopod in any way.
  • The Gup-S reappears for the first time since its debut, over a year before this episode aired.
  • This episode marks the first time that somebody other than Kwazii exits a Gup too early.
  • Peso is revealed to be unable to skilfully drive the GUP-S.