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
Geikie River (Saskatchewan) Fond du Lac River which flows out of the lake to the north-west where it drains into Lake Athabasca which ultimately drains into the Arctic Ocean via the Mackenzie River system, or into the Cochrane River which flows out of the north-eastern side of the lake and into Reindeer Lake which drains via the Churchill River system into Hudson Bay. If Hudson Bay is defined as part of the Atlantic Ocean then the Geikie River is the largest river in the world that drains naturally into two oceans. The Geikie River is bridged by Highway 905 at the highway's 184