The south shore is a big draw for canoeists. The William and MacFarlane Rivers winding past miles of massive golden sand dunes set a scene out of Arabia — though they're dotted with stunted, bonsai-like pines, instead of palms, and skeleton forests once covered with sand, then revealed once again by the shifting dunes. This fragile region is a UNESCO World Heritage Site — and a national treasure.

North shore of Lake Athabasca

The north side of the lake is more rugged, with scattered low islands of shattered granite, sheltered bays, and boreal forest of hardy spruce, pines, and birch. Sometimes, with guidebook in hand, I pick my way carefully over the sharp rocks and pale green reindeer lichen that crunch underfoot, looking for pixie cups, purple horn-toothed moss, bristle mosses, and the enchantingly named"fairy puke." Tougher than they look, a few exquisite alpine flowers bravely bloom in meager soil.

My friend Nora Abercrombie has canoed Lake Athabasca five times. Like most of us, she comes for the primal wilderness here, for its remoteness and isolation.

"It's very peaceful," she says. "I like the bigness of it, and the fact that there's no support. You're really going without a net. When I'm up here I develop this gratitude for little things. Taking away the supports of living in a society is really moving for me.

Her emotional attachment to the lake is understandable. But it's equally clear that there's another draw for her. It has to do with the challenge and sheer exhilaration that comes with living on the edge. And perhaps it has to do with danger.

For there is a caveat to all this wild beauty: Lake Athabasca is not to be taken lightly, and it's never an easy trip. It's not for the faint of heart — or the unprepared. This is a harsh land, Canadian Shield country, where the Precambrian basement rocks are over 600 million years old. Once mountainous, they've been eroded to low hills, scratched and scrawled by the movements of at least five continent-wide ice sheets. And if the land is rough, the lake can be even rougher. Lake Athabasca is the fourth-largest lake entirely within Canada's borders — big enough, some say, to have its own climate. It can be smooth as glass — or an angry, raging sea. Though sunny, windless days are common in midsummer, the weather can change quickly, from glassy calm to six- or eight-foot waves.

"The wind comes up very very fast," says Abercrombie, "and the waves are very, very big. There are several spots on the lake where you can't help but be in a precarious situation, where there's literally nowhere to stop. There's one thirteen-mile stretch on the north shore, along Black Bay on the Crackingstone Peninsula. There are a couple of islands about five miles along, and then there's nothing but sheer rock. That scares me."

It scares me, too. One September day, out fishing at Foster Island — part of an archipelago on the north shore, within eyesight of the dunes to the south — we begin in two-foot waves. Within an hour they have doubled in size, and we realize it's time to head back to camp — or spend the night on the island. Between Foster and Grouse, the next island, the waves double again and I'm pretty scared. In between the heart-stopping moments, though, it's impossible not to see the extraordinary beauty of this place, and be awed by its power.