Storsjöodjuret (or Storsjöodjur) is a lake monster from Swedish folklore.

The creature allegedly lives in Lake Storsjön in the Jämtland province of Sweden.

Lake Storsjön is the largest in central Sweden and the fifth largest in the country. It covers an area of 179 square miles and has a maximum depth of about 240 feet.

The first recorded reference to a monster in Lake Storsjön dates back to the 17th century. The name “Storsjöodjuret” (or Storsjöodjur) first appeared in written records in the late 19th century.

Storsjöodjuret means Great Lake Monster. Some sources refer to the monster as Storsjöormen, meaning Great Lake Serpent.


Storsjöodjuret resembles other lake monsters, such as the Scottish Loch Ness, the American Chessie, Cadborosaurus, and the Argentine Nahuelito.

Storsjöodjuret is a black serpentine monster

Jämtland folklore described the monster as a humped, black serpentine lake monster with a feline (cat-like) or canine (dog-like) head.

Multiple alleged eyewitness accounts estimated Storsjöodjuret at about 11-50 feet long. Some claimed it has fins.

According to cryptozoologist George Eberhart in Mysterious Creatures: A Guide to Cryptozoology (2002), Storsjöodjuret is a serpentine lake monster about 10-45 feet long and about 3-4 feet wide. It has a neck about 8-10 feet long.

The creature has shiny, greenish-to-grayish skin and a dog- or cat-like head. Some reports claimed it has an equine (horse-like) head, large ears, a bushy white mane, and large eyes.

The creature has a long tongue that flicks like a serpent’s tongue.

It has many humps on its back and two pairs of short legs. Some claim it has flippers or side fins instead of legs.

It also has a powerful lashing tail.

Storsjöodjuret is a powerful swimmer

Storsjöodjuret is a fast swimmer. Eberhart estimated its speed in water at about 45 mph. Some alleged eyewitnesses said it makes a loud wailing noise, but others described it as rattling.

In 1997, two sisters who claimed to have seen the creature while swimming in the lake said it had an equine head, a pair of eyes set on the sides of its head, and a neck about 6 feet long.

They added that the body appeared to have scales resembling armor plates.

The creature is reportedly most active during warm weather, which explains why most sightings occur in the summer.

Origin stories

The first reference in Swedish records to a lake monster or lake serpent (sjöorm) associated with Lake Storsjön occurred in a 17th-century manuscript.

Morten Pedersen Herdal manuscript, 1635

The 1635 Morten Pedersen Herdal manuscript tells what could pass as a Storsjöodjuret origin story.

According to the manuscript, the ancient sorcerer and folk hero Kettil Runske used the power of his runes to imprison the monster at the bottom of Lake Storsjön.

Runske achieved the feat by carving a magic spell on the famous Frösö runestone on Frösön, the largest island in the lake.

[Fun fact: According to the Swedish writer Olaus Magnus (1490-1557) in his work, Historia de Gentibus Septentrionalibus (1555), Kettil Runske gained magical powers by stealing the rune staffs from Odin.]

Andreas Plantinus manuscript, 1685

The Anders Plantin or Andreas Plantinus manuscript dated 1685 records another version of the Lake Storsjön monster origin story.

The manuscript refers to a runestone (presumably the Frösö runestone) and claims that beneath it was the head of a serpent monster whose body stretched from Storsjön to a village called Knytta. The manuscript added that the tail was at Hillesand.

The manuscript tells the story of a great serpent that terrorized people crossing Lake Storsjön. It then explained that someone killed the monster and erected the runestone over its body.

[Fun fact: The Frösö runestone on Frösön is Jämtland’s only runestone. It is also Scandinavia’s northernmost runestone. It commemorates the construction of a bridge (c. 1030) and the Christianization of Jämtland. However, the runestone became the subject of local myths and legends.]

The magical trolls Jata and Kata

Another origin story claimed that two trolls, Jata and Kata, used their magical powers to conjure a monster with a snake’s body and a dog’s head.

The two trolls brought their cauldrons to the shore of Lake Storsjön and started brewing magical potions. They spent months working on their magical mixes until one day, a loud sound came from one of the cauldrons and a clap of thunder. And out of one of the cauldrons jumped a monster with the head of a cat and the body of a black snake.

The monster slithered like a lightning bolt across the shore and slid into the lake.

The two mysterious trolls then disappeared in a puff of smoke.

The lake monster soon began terrorizing the people in the area. It grew until it became so big that its coiled body encircled the island in the middle lake.

The people sought help, and the sorcerer Kettil Ruske came to the rescue. He cast a spell carved on a runestone to imprison the beast and raised the stone on Frösön.

Sightings and Tales

There have been multiple reports of Storsjöodjuret sightings. Eberhart reported that most sightings occurred south of Frösön.

Peter Olsson’s Storsjöodjuret book

Interest in the creature inspired Peter Olsson’s 1899 book about it. The book is one of the sources of information about sightings in the 19th century.

One of the earliest reported sightings occurred in 1836 when Aron Andersson and his companions allegedly saw a creature with an equine head and a white mane swimming in the lake away from the shore.

Another early sighting occurred in 1857. According to Swedish newspaper reports, a group working on the lake island saw a strange creature with a cat’s head and a black serpentine body.

In 1893, Marta and Karin Olsson were washing clothes on the shores of the lake when they saw the head of a strange creature bobbing in the water. Karin picked up a pebble and threw it at the monster.

It turned and swam toward the women who fled in fright.

King Oscar II (1829-1907)

Some people tried to capture the monster in the late 1890s. King Oscar II supported some of the efforts, but none succeeded.

Maria Helin

After hearing stories about the strange creature in the lake, Maria Helin led a team to catch it in 1894. King Oscar II heard about Helin and her team and reportedly supported them financially.

She hired a Norwegian whaler, and they set a trap for the creature under a jetty constructed over the lake. It consisted of baited hooks placed strategically in the lake. They gave up after several unsuccessful attempts.

In 1931, Anders Bergqvist and Jonas Hansson reported seeing two humps in the water.

In 1947, Anna Rahm reported seeing a gray, 9-foot creature with a tail, large ears, a flicking tongue, and large eyes.

Carina Johnsson’s photographs and footage

In 1983, Carina Johnsson allegedly photographed a fast-moving creature in the water.

Some locals claimed to have found remains of the embryo of a Storsjöodjuret on the shores of the lake in 1984.

Gun-Britt Widmark reported capturing footage of a creature about 33-39 feet long in 1996.

In 1997, two sisters–Elin and Cecilia Hemreus– claimed they saw the horse-like head of a mysterious creature above the water while swimming in the lake. They also saw loops of the serpentine creature’s body from 30 feet.

A woman claimed to have seen a snake-like creature in the water in 2000. It was swimming about 90 feet offshore and was about 20-25 feet long. It had a dark or black color.

In 2008, a film crew claimed to have used infrared cameras to capture footage of a monster believed to be Storsjöodjuret (see video below).

What is Storsjöodjuret?

Zoologists and cryptozoologists have proposed explanations for the Storsjöodjuret sightings on the premise that people mistook known species or other natural causes for a cryptid monster.

The following are some of the top suggestions:

Unknown aquatic species

In 1899, the Swedish naturalist Peter Olsen, who published a book detailing several eyewitness accounts, suggested that the lake monster was likely an unknown aquatic species, such as a previously unknown species of seal.

Wels catfish

Some zoologists and cryptozoologists proposed that people might have mistaken the Wels catfish (Silurus glanis) for a lake monster.

The Wels catfish or sheatfish is a catfish species widely distributed in freshwater habitats across Europe.

The fish is native to central, southern, and eastern Europe.

It is the largest freshwater fish in all of Europe. Adult specimens may reach nearly 10 feet in length and weigh 200kg. However, most range between 4.5-5.5 feet.

Floating log theory

Some skeptics suggested that people might have mistaken floating logs and other debris for a serpentine monster.

Boat wake theory

Skeptics have also proposed that people might have mistaken wave patterns generated on the water by large bodies (such as boats) for mysterious creatures in the water.

Other Name/sStorsjöodjur, Storsjöormen, Storsie, Storsjö Monster, Storsjoe Monster, Great Lake Monster, Monster of Lake Storsjön, Thelma, Hydogiganta Monstruidae Jemtlandicum
TypeLake Monster


Mysterious Creatures: A Guide to Cryptozoology, George M. Eberhart (2002)., “Sagas and the circum-baltic arena,” accessed on March 7, 2023., “The big sea monster,” accessed and translated from Swedish on March 7, 2023., “Storsjöodjuret: The Great Lake Monster,” accessed on March 7, 2023., “Swedish sea monster ‘caught on film,” accessed on March 7, 2023.

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