The Lagarfljótsormur, Lagarfljót worm, (or simply Iceland Worm Monster) is an Icelandic lake cryptid which is purported to live in the lake Lagarfljót in the town of Egilsstaðir. Sightings have been logged since 1345 and continue into the 21st century, including a 2012 video supposedly showing the creature swimming.
An origin of the creature is given in Jón Árnason's collection of Icelandic folktales and legends published in 1862 and 1864.
The serpentine creature is said to live in Lagarfljót, a freshwater, a below-sea-level, glacial-fed lake which has very poor visibility as a result of siltation. It is described as longer than a bus, or 39 feet (12 m), and has also been reported outside the water, lying coiled up or slithering into the trees. It is a "many humps" type of lake monster, rather than the simply serpentine type of, for example, the Loch Ness Monster.
The Lagarfljót Worm has been sighted several times in modern times, including in 1963 by the head of the Icelandic National Forest Service, Sigurður Blöndal, and in 1998 by a teacher and students at Hallormsstaðir School. In 1983, contractors laying a telephone cable measured a large shifting mass near the eastern shore when performing preliminary depth measurements, and when they later retrieved the non-functional cable, found that it was broken where it had lain over the anomaly:
"This cable that was specially engineered so it wouldn’t kink was wound in several places and badly torn and damaged in 22 different places . . . . I believe we dragged the cable directly over the belly of the beast. Unless it was through its mouth."
In February 2012, the Icelandic national broadcaster, RÚV, published a video thought to show the Lagarfljót Worm swimming in snow-covered icy water. Subsequently this was explained as probably being an inanimate object moved by the rapid current, since it was making no progress through the water. A truth commission reported in August 2014 that members were divided about the video but saw no reason to doubt the existence of the creature, and an expert panel later judged the video genuine.
A sightseeing boat named Lagarfljótsormurinn after it began operations on the lake in 1999, and the Gunnar Gunnarsson Institution in Skriðuklaustur seeks to preserve the traditions of the Lagarfljót Worm for cultural and tourism purposes.
The legend of the worm is first mentioned in the Icelandic Annals of 1345. Sightings were considered to portend a great event such as a natural disaster.
According to the folk tradition recorded by Jón Árnason, the great serpent in Lagarfljót grew out of a small "lingworm" or heath-dragon; a girl was given a gold ring by her mother, and asked how she might best derive profit from the gold, was told to place it under a lingworm. She did so, and put it in the top of her linen chest for a few days, but then found that the little dragon had grown so large, it had broken open the chest. Frightened, she threw both it and the gold into the lake, where the serpent continued to grow and terrorized the countryside, spitting poison and killing people and animals. Two Finns called in to destroy it and retrieve the gold said that they had managed to tie its head and tail to the bottom of the lake but it was impossible to kill it because there was a still larger dragon underneath.
Gases rising from the lakebed create openings in the ice, blow debris from the lake bottom to the surface, and sometimes warp the atmosphere, creating optical illusions. Flotsam from the mountain sides and glaciers also collects in tangles that can look like some sort of monster. According to Helgi Hallgrímsson, an Icelandic biologist who has extensively studied the lake, both of these could explain some but not all of the sightings, while traditional legendary material could explain some of the stories.