The Mackenzie River flows north through Canada’s Northwest Territories, from the boreal forest surrounding Great Slave Lake to the treeless tundra where it empties into the Arctic Ocean. During spring runoff, great spruce logs float north and wash up in piles. Traditionally the Inuvialuit—the Inuit of Canada's western Arctic—would collect this driftwood to build sod houses in their settlements, covering the timber in living grass and soil that insulated against harsh Arctic winters