This ecoregion extends westward from Thunder Bay to Sioux Lookout and Rainy Lake in northwestern Ontario. It is marked by warm summers and cold winters. The mean annual temperature is approximately 1°C, but can rise up to 2°C near Lake Superior. The mean summer temperature is 14°C and the mean winter temperature is -13°C. The mean annual precipitation ranges 700-800 mm. This ecoregion is classified as having a moist low boreal ecoclimate. The dominant vegetation is a combination of coniferous and mixed forests with coniferous forests dominant in the western portion of the ecoregion. Characteristic species of the coniferous forests are white spruce, balsam fir, and eastern white pine. Subdominant species include trembling aspen, paper birch, and jack pine. Warmer sites, dominated by mixed forests, are characterized by red and sugar maple, and yellow birch. Warmer and drier sites are dominated by jack and red pine, and paper birch. Poorly drained sites are characterized by black and white spruce, balsam fir, tamarack, eastern red cedar, and willow. The ecoregion is underlain by massive, crystalline, acidic, Archean bedrock forming hummocky, broadly sloping uplands and lowlands. It includes southern Port Arthur Hills, formed of Proterozoic sills and sediments tilted to the south, forming dissected cuestas and ridges. Sandy fluvioglacial and clayey lacustrine deposits occur throughout. Small to medium-sized rock-bound lakes are more numerous in its western section, and many are linked by bedrock-controlled networks of streams and drainageways flowing westward into the Lake of the Woods. Bedrock outcroppings are common, and Dystric Brunisols are the dominant soils on discontinuous, sandy morainal deposits in the uplands. Significant inclusions are Gray Luvisols on the fine-textured sediments and Mesisols and Fibrisols on peat-covered, poorly drained lowlands. Characteristic wildlife includes moose, black bear, lynx, snowshoe hare, wolf, and white-tailed deer. Bird species abound, including the American black duck, wood duck, hooded merganser, and pileated woodpecker. Major land uses include forestry, water-oriented recreation, and tourism. There is mixed farming in the southeast near Thunder Bay. The major communities include Thunder Bay and Atikokan. The population of the ecoregion is approximately 135 800.
This ecoregion is part of the Boreal Shield ecozone.