While most of Alberta's rivers originate within Alberta, some have their headwaters in places like Montana (Waterton, St. Mary, Milk), British Columbia (Wapiti, Peace), and Saskatchewan (Clearwater, Cold Lake). The rivers that originate or flow through Alberta eventually end up in one of three places: the Arctic Ocean via the Mackenzie River Basin, Hudson Bay via the Nelson or Churchill River Basins, or the Gulf of Mexico via the Missouri-Mississippi River Basin. The volume of water that flows in these continental river basins varies greatly.

Clear River at Highway 64

Most of the water flowing in Alberta's rivers (almost 87 percent) flows northward via the Mackenzie River Basin. Major rivers within Alberta that contribute to the flow of the Mackenzie River Basin include the Slave River, Peace River, Athabasca River/Lake Athabasca and the Smoky River, which individually are the four largest rivers in the province. Other major tributaries to these rivers are the Clearwater River, Wapiti River, Wabasca River and the Lesser Slave River/Lesser Slave Lake.

Rivers flowing into the Nelson or Churchill basins, and ultimately into Hudson Bay, account for 13 percent of the flow in Alberta's rivers. Major rivers within Alberta that contribute to the flow of the Churchill River Basin include the Beaver River and the outflow from Cold Lake. Major rivers within Alberta that contribute to the flow of the Nelson River basin include the South Saskatchewan River, North Saskatchewan River, Red Deer River, and Battle River. This also includes significant tributaries like the Bow River, Oldman River, St. Mary River and the Brazeau River.

Rivers flowing into the Missouri-Mississippi basin, and ultimately into the Gulf of Mexico, account for about 0.1 percent of Alberta's natural river flows. The largest river in Alberta that is part of this basin is the Milk River. The Milk River originates in the United States, flows through Alberta and then flows southward out of Alberta into Montana. Other Alberta rivers that are part of the Missouri-Mississippi basin include Lodge Creek and Battle Creek, with their headwaters in the Cypress Hills of south eastern Alberta.

View a map of the province showing the continental basins, the relative sizes of rivers and the natural flows into and out of the province by clicking on the thumbnail below. A table of the long-term average natural flow volumes for the largest Alberta rivers is also shown below.

The values in the table are based on the long-term average streamflows. As the total volume of natural flow in a river varies from year to year due to varying climate patterns, the table also provides a summary of the historic maximum and minimum annual natural runoff volumes for each river that we have observed. This gives you an idea of the natural range of flow variability at each location.

If you would like more detailed information on historical streamflows and trends in Alberta's major rivers, you can download this pdf report (1.9 MB) from the Information Centre. For more information on how climate patterns and natural variability affects streamflow, visit the water quantity influences section.