The river discharges more than 325 cubic kilometres (78 cu mi) 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 the larger lakes, such as Great Slave, ice can persist as late as mid-June.
The river typically freezes by late October or November, starting in the north.
Year round, the Mackenzie's outflow has a major stabilizing effect in the local climate above the Arctic Ocean with large amounts of warmer fresh water mixing with the cold seawater.

The average flow rate at the mouth is 9,910 m³/s (350,000 cu ft/s), the second largest in Canada after the St Lawrence, and the fourteenth largest in the world.
About 60 percent of the water comes from the western half of the basin, which includes the Rocky, Selwyn, and Mackenzie mountain ranges out of which spring major tributaries such as the Peace and Liard Rivers, which contribute 23 and 27 percent of the total flow, respectively.
In contrast the eastern half, despite being dominated by marshland and large lakes, provides only about 25 percent of the Mackenzie's discharge.

During peak flow in the spring, the difference in discharge between the two halves of the watershed becomes even more marked.
While large amounts of snow and glacial melt dramatically drive up water levels in the Mackenzie's western tributaries, large lakes to the east retard springtime discharges.
Spring floods 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 gauges at several upstream points along the Mackenzie River.
The average flow rate at the outlet of Great Slave Lake is 4,269 m³/s (150,800 cu ft/s).
At Fort Simpson, below the Liard River, it is 6,769 m³/s (239,000 cu ft/s).
At Norman Wells it is 8,446 m³/s (298,300 cu ft/s), and at the Arctic Red confluence it is 8,926 m³/s (315,200 cu ft/s).
The river discharges more than 325 cubic kilometres (78 cu mi) 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 the larger lakes, such as Great Slave, ice can persist as late as mid-June. The river typically freezes by late October or November, starting in the north. Year round, the Mackenzie's outflow has a major stabilizing effect in the local climate above the Arctic Ocean with large amounts of warmer fresh water mixing with the cold seawater.
The average flow rate at the mouth is 9,910 m³/s (350,000 cu ft/s), the second largest in Canada after the St Lawrence, and the fourteenth largest in the world. About 60 percent of the water comes from the western half of the basin, which includes the Rocky, Selwyn, and Mackenzie mountain ranges out of which spring major tributaries such as the Peace and Liard Rivers, which contribute 23 and 27 percent of the total flow, respectively. In contrast the eastern half, despite being dominated by marshland and large lakes, provides only about 25 percent of the Mackenzie's discharge.
During peak flow in the spring, the difference in discharge between the two halves of the watershed becomes even more marked. While large amounts of snow and glacial melt dramatically drive up water levels in the Mackenzie's western tributaries, large lakes to the east retard springtime discharges. Spring floods 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 gauges at several upstream points along the Mackenzie River. The average flow rate at the outlet of Great Slave Lake is 4,269 m³/s (150,800 cu ft/s). At Fort Simpson, below the Liard River, it is 6,769 m³/s (239,000 cu ft/s). At Norman Wells it is 8,446 m³/s (298,300 cu ft/s), and at the Arctic Red confluence it is 8,926 m³/s (315,200 cu ft/s).
Mackenzie River