Loch Ness monster. Computer artwork of the Loch Ness Monster swimming. Sightings of the monster have occurred at least since the 15th century, with earlier stories dating to the 6th century, but scientific evidence for its existence is lacking. Often the creature is said to resemble a plesiosaur (a prehistoric marine reptile), with a long, elegant neck, small head, and flippers. Sceptics have suggested that the sightings are of nothing more than unstable masses of drifting peat. However, the monster's alleged existence continues to attract tourists, and the myth endures.