By Paul Sieveking.

SWEDEN'S most famous lake monster, the Storsjoodjuret (the monster of Lake Storsjon) had a lot of coverage in the Swedish newspapers last summer following a video recording of the creature in July by Gun-Britt Widmark, 67, while boating on the lake off Ostersund with a party of pensioners. Whatever it was had humps and was 33 to 39 feet long.

Four people made a further sighting on July 22 from their verandah overlooking the lake. They watched a long, wave-like movement in the water, like the wash of a boat, though there was no boat in sight. Through binoculars they saw something rolling up and down in the water, breaking the surface every three seconds. It moved parallel with the Rodo bridge for a couple of minutes, then changed direction by 90 degrees, finally diving and disappearing under the bridge. One of them tried to capture the phenomenon on video, but it was too far away. Sten Rentzhog, director of the local Ostersund museum, has collected nearly 500 accounts of Storsjoodjuret sightings dating back to 1635. In recent years, most of these have coincided with the summer tourist season, leading sceptics to suspect a degree of public relations hype; but last July the paper Ostersunds Posten complained that the monster was poorly marketed compared with Nessie or some of the American lake monsters. There was no merchandise on sale apart from two postcards. Furthermore, the monster was seasonal long before there were any tourists, as can be seen from Dr Peter Olsson's study of 1899.

The folkloric explanation is that the lake monsters of this part of Sweden are seasonal because they migrate from the Gulf of Bothnia, where they spend the winter months, and it was said that sometimes in summer they were observed on land moving between the various lakes. Incidentally, Dr Olsson wondered if the monster might be an unknown species of giant seal, but readily admitted that seals should have been more noticeable in the winter, and noted the lack of breathing holes in the lake's ice.

In 1986, after 22 years of sporadic debate, the county administration of Jamtland (the district which encompasses the lake) declared that anyone trying to capture or kill the Storsjon monster could be prosecuted. The ruling had taken such a long time because lawyers required an "official" Linnaean name for the animal and naturally the zoological establishment would not acknowledge that the creature existed.

No one could decide if the matter should be dealt with under the Game Act or the Fishery Regulation Act. Scandinavian sophistry overcame the conundrum by invoking the Nature Conservation Act, prohibiting any threat to the unknown creature "while awaiting a determination of its species". This was prudent, as descriptions of the monster have changed over the years.

In the 19th century, nearly all the witnesses described a "waterhorse", its head surrounded by a long white mane floating in the water. Contemporary witnesses don't seem to notice its horse-like head and mane. My Swedish correspondent dryly describes the beast as a "camouflageon" - a hitherto unknown species of highly developed amphibian chameleon.

Olle Mattsson, an antiquarian at the Ostersund museum, has spent the last two years examining the museum's archives for historical observations of the monster, to which he has added many interviews with modern witnesses. His version of the "typical" monster is 10 to 16 feet long, 12 to 16 inches wide, dark grey or black with a small head. "All evidence indicates that there is a population [of the monsters]," he said. "They probably move together in a pack."

Although the local papers report two or three sightings every summer, Mr Mattsson believes that most witnesses keep quiet out of fear of ridicule - which seems rather odd, considering the large number of witnesses who have come forward. This is probably a modern gloss on the old taboo against mentioning encounters with the dangerous or unknown, especially to strangers.