Mackenzie River from the Peace-Athabasca system are significantly slowed by the delta area at the western end of Lake Athabasca causing the lake to rise, and the excess water can only flow out after the rivers have receded. The same phenomenon occurs at Great Slave Lake, which naturally regulates the flow from the Slave River into the Mackenzie. There are river gages at several upstream points along the Mackenzie River. The average flow rate at the outlet of Great Slave Lake is . At Fort Simpson, below the Liard River, it is . At Norman Wells it is , and at the
Boats of the Mackenzie River watershed Landing north of Edmonton to the Slave River rapids, the only significant obstacle en route to the Mackenzie. In 1886, the S.S. "Wrigley" was launched on the other side of these rapids, at Fort Smith, and for the first time a steam-driven vessel operated on the Mackenzie River as far as Aklavik in the river delta before it spilled into the Arctic Ocean. A series of small portage trails were established between Smith's Landing (later Fort Fitzgerald) and Fort Smith to skirt the 16-mile rapids - this was later upgraded into a full road in the 1920s. In 1898 the