Footage has emerged showing what appears to be a giant serpent swimming against the current through an Icelandic lake.

The creature is speculated to be the Icelandic equivalent of the Loch Ness Monster, Lagarfljótsormurinn, or Lagarfljóts Worm, which can be traced all the way back to 1345, Iceland Review reports.

According to legend, the monster grew from a tiny magical worm that had been placed in a ring of gold to make it grow, IceNews said.

Instead of enlarging the gold, the worm grew into a giant snake and both it and the ring were tossed into the Lagarfljó, where it continued to grow to monstrous proportions.

Sightings of the worm are considered to be a bad omen.

The video was shot by Hjörtur Kjerúlf and was first posted on ruv.is.

Skeptics have claimed all the video shows is a torn fishing net that froze in the 140km long river.