A search by a team of monster-hunters failed on Sunday to find any traces of a mysterious creature said to have inhabited Sweden's Great Lake for at least 360 years.

A fleet of 15 vessels with researchers and six divers set off from Ostersund in Jamtland County, central Sweden, early on Sunday equipped with an underwater video camera and echo equipment hoping to solve the centuries-old mystery. But project spokesman Anders Brattgra said the search, the most extensive ever of the Great Lake, failed to find the infamous monster — but researchers have not yet given up hope.

"We didn't find a lake monster. The Great Lake is certainly no Jurassic Park," Brattgra told Reuters by phone from the banks of the lake. "But a lot of people have seen something in the lake and they are not fools. They have seen something that they cannot explain so the mystery remains. We have decided we may do somthing again next year."

The town of Ostersund, 600 km (370 miles) northwest of Stockholm on the banks of Sweden's fifth-largest lake, has been puzzled for centuries about reported sightings of a horse or snake-like creature in the Great Lake. Sightings of the monster, Sweden's answer to Scotland's Loch Ness monster, has been reported on 150 occasions by 450 people since 1635 when a local parson mentioned the creature in a parish register. By the late 19th century the frequency of sightings rose and in 1894 a group from Ostersund set up the company to capture the Great Lake Monster tried unsuccessfully to track down the animal, using traps baited with pigs and calves. The most recent sighting was in early July this year when a local man spotted something on the surface of the water as he watched a home video he had taken of the town's new bridge. The video was aired on national television.

Brattgra said this year's effort was by far the largest search to date and involved British specialist Adrian Shine, who has hunted for Loch Ness's monster, Nessie, for the past 20 years. "We have ruled out that the creature is a mammal as the lake is frozen over in the winter and it would not be able to breathe but it could be a big fish," Brattgra said. "Various spots come up on the echo recording equipment but no one could tell what it was monitoring."

He said very little was known about the Great Lake, which is very large and as deep as 100 meters in parts. The search on Sunday covered just over five square kms or about one percent of the lake. Witnesses' reports fall into two distinct categories. Some report seeing a large eel about three meters (10 feet) long and one meter (three feet) wide that is grey-brown while others report a large serpent of up to 14 meters (46 feet) with humps and a small dog-like head.

In 1986 the county administration of Jamtland declared anyone trying to capture, injure or kill the monster could be prosecuted under the Nature Conservancy Law.