What lies beneath? That’s the deep secret of Great Slave Lake, whose mysterious, watery oblivion is unrivalled in North America. If you sail offshore from the community of Łutselk’e, on the lake’s fabled East Arm, you’ll find yourself bobbing in water at least two-thirds of a kilometre deep – making this the deepest lake on the continent and the sixth deepest on Earth. How deep, exactly? Weirdly, we don’t know. For a long time, the official figure was 614 metres – enough to sink the CN tower. But recently, researchers discovered even deeper spots down there, plunging another 30 metres or more. Here’s what you can be sure of: This cold, wet abyss is heaven for supersized trout. Fifty-pounders are commonplace in Great Slave. And far-larger fish – perhaps of world-record size – are likely lurking in the depths, just waiting to be caught.