Boundaries

This ecoregion occurs in eastern British Columbia, northern Alberta, northwestern Saskatchewan and southern Northwest Territories (NWT). It includes areas in the upper portion of the Mackenzie basin that are drained by the Hay and Slave rivers that flow into Great Slave Lake, the Peace River that flows into the Slave River, and the Athabasca River that flows into Lake Athabasca.

Topography

The foothills of western Alberta rise above the plains, mainly as linear ridges, rolling plateau remnants, and broad valleys. To the east, the ecoregion is underlain by Cretaceous shale and covered with undulating glacial till. The sloping land surrounding the Peace River is underlain by sandstone and shale and is covered by sediments of sand and till. The Slave River lowland is underlain by relatively level Palaeozoic carbonates forming sandy plains, or limestone bedrock covered with silts, clays and extensive peat deposits.

Freshwater habitats

Many of the rivers in this ecoregion begin as fast-flowing streams with headwaters in the Rocky Mountains. Much of the ecoregion to the east of the Rockies is classified as wetlands. The Peace River cuts deeply through the plains of northern Alberta and, in certain locations, the valley extends up to 11 km in width. The Slave River has a winding, multi-channeled course through the flat terrain of the Canadian Shield before entering the grassy wetlands of the delta on the south shore of Great Slave Lake. The Peace and Slave rivers and lakes Athabasca and Claire form the Peace-Athabasca Delta, one of the largest inland freshwater deltas in the world. 

The Athabasca River begins in the Columbia Icefields in Jasper National Park where it is recognized as a Canadian Heritage River. The river flows through mountains with gorges, rapids, waterfalls and narrow channels before opening into wide, braided streams with alluvial flats. It winds through prairies and muskeg before entering Wood Buffalo National Park and Lake Athabasca. 

Great Bear, Great Slave, Lake Athabasca and a chain of lakes between them are remnants of a single postglacial lake. Lake Athabasca is at the edge of the Precambrian Shield and is a cold, deep lake. Lake Claire was also once a clear, deep lake but has become much shallower due to siltation.

Terrestrial habitats

This ecoregion intersects the following terrestrial ecoregions: Alberta-British Columbia Foothills Forests, Canadian Aspen Forests and Parkland, Mid-continental Canadian Forests and the Muskwa-Slave Lake Forests. Along the Hay and Athabasca rivers, vegetation is transitional between boreal and Cordilleran, and is characterized by mixed forests of lodgepole pine (Pinus contorta), quaking aspen (Populus tremuloides), white spruce (Picea glauca), balsam poplar (P. balsamifera), paper birch (Betula papyrifera) and balsam fir (Abies balsamifera). Black spruce (P. mariana) and tamarack (Larix laricina) are found in wet sites. Vegetation along the Peace River drainage includes large stands of quaking aspen (Populus tremuloides), followed to a lesser extent by balsam poplar (P. balsamifera). Jack pine (Pinus banksiana) stands may be found in dry, sandy areas. To the south of Great Slave Lake is a continuous mid-boreal mixed coniferous and deciduous forest extending from northwestern Ontario to the foothills of the Rocky Mountains. This forest includes quaking aspen (Populus tremuloides), balsam poplar (Populus balsamifera), white and black spruce (Picea glauca and P. mariana), and balsam fir (Abies balsamea), with ericaceous shrubs (Ericaceae) and mosses.

Description of endemic fishes

No known endemic species.

Ecological phenomena

As the result of physical barriers, the species in this ecoregion generally do not exhibit diadromy. The Peace-Athabasca Delta, recognized as a Ramsar wetland complex of international importance, is one of the largest inland freshwater deltas in the world.

Justification for delineation

The ecoregions of Canada were identified based on the faunal similarity of 166 major watersheds based on a cluster analysis of freshwater fish occurrences in these watersheds. The Upper Mackenzie ecoregion includes the upper Mackenzie River watershed. The fish fauna of the Mackenzie watershed is a mix of fishes from the northwestern Berinigian refugium and southern Mississippian refugium. However, it has a lower diversity than the Lower Mackenzie [105] ecoregion, as the falls separating the two ecoregions prevent the upstream migration of some diadromous species.

Level of taxonomic exploration

Fair / Poor