Western Hudson Bay




Mary Burridge and Nicholas Mandrak



Major Habitat Type

Polar freshwaters

Drainages flowing into

All rivers flow into the Arctic Ocean via Hudson Bay.

Main rivers to other water bodies

The largest river system in this ecoregion is the Thelon River (904 km). It begins in Lynx Lake, NWT, flows through Beverly, Aberdeen, Schultz, and Baker lakes in Nunavut, and empties into Chesterfield Inlet, Hudson Bay. Its main tributaries are the Dubawnt River ( 842 km), which joins the Thelon River at Beverly Lake, and the Kazan River (850 km), which enters the Thelon River at Baker Lake. Drainages further south include the Thlewiaza River that begins in Manitoba and flows through Nueltin Lake into Hudson Bay. The North and South Seal rivers join at Shethanei Lake to form the Seal River. The main tributary of the Seal River is the Wolverine River.

Wollaston and Reindeer lakes are also located in this ecoregion.



This ecoregion occurs in northeast Saskatchewan, northern Manitoba, southeastern Northwest Territories (NWT), and much of the mainland of Nunavut. Major drainages include the Thelon, Thlewiaza, and Seal rivers.


The western part of this ecoregion is underlain by flat-lying Paleozoic and Mesozoic sedimentary bedrock, with lowland plains of glacial moraine and marine deposits. Chesterfield Inlet is a fjord that stretches inland 160 km from Hudson Bay to the Thelon River. It marks a physiographic divide between a narrow, rocky coastal plain with hilly terrain to the north, and an expanse of low relief and poorly developed drainage to the south. Further south the ecoregion is underlain by Precambrian granitic bedrock, with broadly rolling uplands and lowlands studded with numerous lakes, ponds, and wetlands. Bedrock outcrops are common, and there are long eskers reaching lengths of up to 100 km in places.

Freshwater habitats

The Thelon River, the largest unaltered drainage basin emptying into Hudson Bay, winds through a broad valley lined with thick stands of spruce. The Seal River originates at Shethanei Lake where sand-crowned eskers are typical of much of the landscape. The river accelerates into rapids and gorges at Great Island, and then flows through a transitional subarctic zone into arctic tundra. Here, the Seal passes through huge boulder fields and complex rapids before flowing into Hudson Bay. Many of the lakes, including Reindeer, Wollaston, Nueltin, and Dubawnt, are characteristic Canadian Shield lakes with irregular shorelines, numerous islands, and clear and deep waters. Lakes in the northern part of this ecoregion are icebound most of the year. Wetlands are common in lowlands throughout the ecoregion.

Terrestrial habitats

This ecoregion spans a transition zone between tundra and boreal forest. To the north vegetation is sparse and dwarfed due to a harsh climate and shallow soil. Arctic willow (Salix arctica) is present with saxifrage (Saxifraga spp. ) and lichens. Vegetation is greater on wet sites along coastal lowlands, sheltered valleys, and along rivers and streams. Further south there is a continuous cover of shrubby vegetation with stunted black spruce (Picea mariana), tamarack (Larix laricina), white spruce (P. glauca), dwarf birch (Betula spp.), willow (Salix spp.), ericaceous shrubs (Ericaceae), cottongrass (Eriophorum spp.), lichens, and moss. 

Description of endemic fishes

There are no known endemic species within the ecoregion.

Ecological phenomena

The Arctic char (Salvelinus alpinus) and, occasionally, lake trout (S. namaycush)exhibit anadromy between Hudson Bay and its tributaries. Harbour Seals (Phoca vitulina), normally found in salt water, are found up to 200 km upstream from Hudson Bay, in the Seal River.

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 Western Hudson Bay ecoregion is comprised of watersheds draining into western Hudson Bay. The fish fauna is a mix of fishes from the northwestern Berinigian refugium and southern Mississippian refugium, but lacking some of the diadromous species found in the Arctic drainages.

Level of taxonomic exploration



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