A fleet of 15 vessels with researchers and six divers set off from Ostersund in central Sweden equipped with an underwater video camera and echo equipment, trying to spot the mosnter, variously described as a grey-brown eel about 10ft long and 3ft wide or a serpent of up to 46ft long with humps and a small dog-like head.
Project spokesman Anders Brattgra said the search, the most extensive ever of the Great Lake, failed to find the monster - but researchers have not yet given up hope.
"We didn't find a lake monster. The Great Lake is certainly no Jurassic Park," Mr Brattgra said. "But a lot of people have seen something in the lake and they are not fools.
"We have decided we may do something again next year."
Ostersund, 370 miles north-west of Stockholm, has been puzzled for centuries about reported sightings of the horse- or snake-like creature.
Sweden's answer to Scotland's Loch Ness monster has been allegedly sighted on 150 occasions by 450 people since 1635, when a local parson mentioned the creature in a parish register.
The most recent sighting was last month when a local man watching a video he had taken of the town's new bridge spotted something strange on the surface of the water.
Mr Brattgra said this year's effort was by far the largest search to date and involved British specialist Adrian Shine, who has hunted for the Loch Ness Monster for20 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," said Mr Brattgra.
"Various spots come up on the echo recording equipment but no one could tell what it was monitoring."Reuse content