Storsjöodjuret (Swedish pronunciation: [ˈstuːʂøːuˈjʉːrɛ], literally "The Great-Lake Monster") is a lake monster reported to live in the 300-foot-deep (91 m) lake Storsjön in Jämtland in the middle of Sweden. The lake monster was first reported in 1635 and is the only one of its kind in Sweden. When the only city located by Storsjön, Östersund, celebrated its 200 year anniversary in 1986 Storsjöodjuret along with its offspring and nest became protected by law, a law which was revoked in 2005.
Storsjöodjuret is described as a serpentine or aquatic reptile with fins across its back and the head of a dog. It is reported to measure approximately six meters long, and some accounts describe it as having several humps.
The first description of a sea creature in Storsjön was made in a folklorist tale by vicar Morgens Pedersen in 1635.
"A long, long time ago two trolls, Jata and Kata, stood on the shores of the Great-Lake brewing a concoction in their cauldrons. They brewed and mixed and added to the liquid for days and weeks and years. They knew not what would result from their brew but they wondered about it a great deal. One evening there was heard a strange sound from one of their cauldrons. There was a wailing, a groaning and a crying, then suddenly came a loud bang. A strange animal with a black serpentine body and a cat-like head jumped out of the cauldron and disappeared into the lake. The monster enjoyed living in the lake, grew unbelievably larger and awakened terror among the people whenever it appeared. Finally, it extended all the way round the island of Frösön, and could even bite its own tail. Ketil Runske bound the mighty monster with a strong spell which was carved on a stone and raised on the island of Frösön. The serpent was pictured on the stone. Thus was the spell to be tied till the day someone came who could read and understand the inscription on the stone."
Another legend was written down by the prolocutor Andreas Plantin in an inquiry in 1685.
"It is said that beneath this [rune]stone lies a dreadfully large head of a serpent and that the body stretches over Storsjön to Knytta by and Hille Sand where the tail is buried. The serpent was called a rå and therefore shall this stone be risen. Since no one peacefully could cross [Storsjön], the ferryman and his wife states, along with many others, that in the last turbulent time this stone was tore down and broken in two. As long as this stone laid on the ground many strange things occurred in the water, until the stone was risen and assembled anew."
The runestone both texts refer to is the Frösö Runestone, the northern-most raised runestone in the World. However while a large serpent is indeed pictured on the stone there is no reference about it nor "Ketil Runske" in the text itself, which instead tells about Austmaðr, Guðfastr's son's christening of Jämtland. Though it has indeed been broken in two pieces.
Common interest in the creature was sparked first in the 1890s. After several sightings, an enterprise of locals was founded to catch the monster, even drawing the support from king Oscar II. Since then hundreds of monster sightings have been made. No scientific results have been made, but the supporters have never lost their faith.
In August 2008 a group of filmers claimed to have captured Storsjöodjuret on film. The cameras showed red so it was something endothermic that was filmed.
In 1986, the Jämtland county administrative board declared the Storsjöodjuret to be an endangered species and granted it protected status. However, it was removed from the list in November 2005.