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
Steamboats of the Peace River Steamboats of the Peace River The Peace River, which flows from the Rocky Mountains in British Columbia to the Peace–Athabasca Delta and Lake Athabasca in Alberta, was navigable by late nineteenth and early twentieth century steamboats from the Rocky Mountain Falls at Hudson's Hope to Fort Vermilion, where there was another set of rapids, then via the lower Peace from Vermilion to Lake Athabasca. The Peace is part of the Mackenzie Basin, a larger river complex which includes the Athabasca, Slave, and Mackenzie Rivers. The Athabasca had large rapids too at Grande Rapids and Fort Smith; in this way the