Netflix's 'Below': The Truth About the Giant Sea Creature Josh Hartnett Battles in New Limited Show

Netflix's new limited series Below sees Josh Hartnett facing a terrifying sea creature threatening an isolated Newfoundland fishing community. But while the monster at the centre of the six-episode thriller is fictional, some of its characteristics draw on real marine biology.

Released on 8 October 2026, the series follows fisherman Calvin Penney (Hartnett), who teams up with visiting marine biologist Fonda Howander (Mackenzie Davis) to investigate a series of mysterious underwater attacks. Charlie Heaton plays Calvin's son, Wade Penney, as the family and their community confront a threat emerging from the sea.

Created by Jesse McKeown, Below also explores environmental change, the struggle to preserve a traditional fishing community and the secrets hidden beneath its waters.

Could the Giant Sea Creature in 'Below' Really Exist?

The creature, known as Mudder, is a giant cephalopod — a group of marine animals that includes squid and octopuses. Although giant squid are real, the aggressive behaviour depicted in the series is far removed from what scientists generally understand about these elusive deep-sea animals.

Netflix consulted marine biologist Dr Annie Mercier of Memorial University's Ocean Sciences Centre in Newfoundland to help fact-check the series' science. Mercier also inspired the character of Fonda. According to Mercier, giant squid average around 33 feet in overall length, with their long feeding tentacles contributing substantially to that measurement. Their eyes are among the largest in the animal kingdom, and their deep-water habitat makes them notoriously difficult to observe and study.

Despite their intimidating size, giant squid are not known to behave like the monster portrayed in Below. Mercier described it as 'very improbable' that these deep-sea creatures would leave their natural environment to attack humans above water.

'They don't have the strength in their skeleton to do any harm to something that's above water,' she explained in an interview. Mercier added that squid are generally more likely to retreat than confront humans, although an animal protecting its offspring could behave more aggressively under certain circumstances.

What Is Mudder Protecting?

As the mystery unfolds, Mudder's apparent hostility is revealed to be connected to her egg sac, which is trapped in an iceberg. In the series, the water is becoming too warm for her unborn offspring to survive, prompting her increasingly desperate behaviour.

The iceberg is central to the story: as it melts, material associated with Mudder spreads into the local water supply, contributing to the strange symptoms experienced by residents. The creature's predicament is also tied to the series' wider environmental themes.

However, Mudder's specific circumstances are fictional. The storyline should not be taken as evidence that giant squid universally respond to warming oceans in this way or that their eggs cannot survive in warmer water under all circumstances.

The plot does draw on genuine cephalopod reproductive behaviour. Some cephalopod species guard their egg masses for extended periods, tending to and aerating them while reducing or stopping their own feeding. This demanding process can continue for months, and some species die after reproduction.

These behaviours provide a real biological reference point for Mudder's protective instincts, even though her particular situation belongs to the series' fictional world.

The Real Science Behind 'Below's Environmental Themes

Climate change is another important part of the series. Mercier explained that rising ocean temperatures and changes in water chemistry can affect marine animals and the environments they depend on.

Warmer water generally holds less dissolved oxygen than colder water, while ocean acidification and other changes in water chemistry can place additional pressures on marine ecosystems. The effects vary by species and habitat, influencing where marine animals can live and how well they survive.

In Below, these environmental pressures are woven into the story of a fishing community already struggling with change. Mudder's plight gives the thriller an emotional dimension, encouraging viewers to reconsider whether the creature is simply a threat or another living thing caught in a changing environment.

The series also reflects how little is known about some deep-sea species. Giant squid remain difficult to study because they live far below the surface, and scientists may struggle to understand marine animals before their habitats are significantly altered.

Is Mudder Based on a Real Animal?

Ultimately, Mudder is a fictional monster inspired by the real world of giant squid and other cephalopods. The animals' size, intelligence, elusive nature and reproductive behaviours provide a scientific foundation for parts of the story, but the creature's attacks and its specific connection to a warming iceberg are dramatic inventions.

By combining marine biology with a story about family, community and environmental change, Below turns a conventional sea-monster thriller into something more complicated: a tale in which understanding the creature may be just as important as surviving it.