Mackenzie River great depths to bedrock. A characteristic feature of the delta is its numerous pingos, or hills of earth-covered-ice – some 1,400 of them. The Peel River, carrying much of the runoff from the northern Yukon, joins in the delta at a point northeast of Fort McPherson. Below there, the Mackenzie diverges into several large channels with the largest heading north-northeast, emptying into the Beaufort Sea west of Tuktoyaktuk. At , the Mackenzie River drainage basin encompasses nearly 20 percent of Canada. About , or 54 percent of the basin, lies above Great Slave Lake. Permafrost underlies about three-quarters of the
Mackenzie River . Six other lakes in the watershed cover more than , including the Williston Lake reservoir, the second-largest artificial lake in North America, on the Peace River. The river discharges more than of water each year, accounting for roughly 11% of the total river flow into the Arctic Ocean. The river is frozen for most of the year, with the ice typically breaking up by early to mid-May in the south, and late May-early June in the north. Ice breaks up earlier on the tributaries, sometimes causing ice jams and flooding where they meet the Mackenzie. In the middle of