Somewhere in the murky depths of the continent's deepest lake, a monster lurks. Jim Lynn is sure of it.This week, the Roman Catholic priest was looking out from his home on the shores of Great Slave Lake near Yellowknife when he saw an object trailing a small boat across the water."I got the goggles because it was moving fast and I was kind of curious as to what it was," said Lynn, 66. "It was high, six to eight feet above the water and moving at an incredulous speed."It was like the head of a dragon -- just coming out of the water at just a ferocious speed, just moving like crazy."Lynn watched as the creature, which looked green, hurtle behind an island, then disappear. He quickly called the Yellowknifer, a local newspaper, to place a advertisement asking the person on the lake that day to call him."I would think they would have felt the waves (from the creature)," he said.Step aside, Nessie and Ogopogo, there's a new mystery leviathan on the block. And according to Chris Woodall, it's called Ol'Slavey.Woodall, a Yellowknifer columnist, wrote earlier this summer that Great Slave Lake, with a maximum depth of 614 metres, hides some weird and wonderful creature.To his surprise, his phone soon started ringing with calls from people who claimed to have seen just such a thing. He gave thecreature the name Ol'Slavey, after one of the aboriginal languages in the Northwest Territories.It's a fitting name, since the Dene have many stories about an unknown creature in the waters.