This ecoregion extends from Herchmer in northern Manitoba to James Bay, and includes Akimiski, North Twin and South Twin islands in northern Ontario. The ecoregion is marked by short cool summers and very cold winters. The mean annual temperature is approximately -3.5°C. In Manitoba the mean annual temperature can exceed -5°C. The mean summer temperature is 11°C and the mean winter temperature is -18.5°C. The mean annual precipitation ranges from less than 500 mm in the west to less than 700 mm near James Bay. The ecoregion has a low subarctic ecoclimate. Stands are denser and trees are larger than in the coastal ecoregion to the north. The vegetation cover is dominated by open stands of stunted black spruce, tamarack and white spruce. The shrub layer consists of dwarf birch, willow and northern Labrador tea. The ground cover is dominated by cottongrass or by moss and lichen. Dry sites often support open stands of white spruce with an ericaceous shrub layer, and a ground cover of lichen. Poorly drained sites have vegetation characterized by sedge and cottongrass tussocks or sphagnum hummocks. Balsam poplar, white spruce and paper birch are common along rivers. The ecoregion is part of the Hudson Bay Lowland, and is controlled by flat-lying Palaeozoic limestone bedrock, that slopes gently northeastward and eastward to Hudson Bay. The maximum elevation is about 120 m asl in the south. This area was also inundated by the postglacial Tyrrell Sea and covered by marine sediments. Gradual uplifting continues in this region as well. The ecoregion is an extensive, wet, flat plain characterized by poorly drained peatlands and small lakes, ponds, and creeks. The wetlands cover up to 75% of the area and consist of peat plateau and palsa bogs, and horizontal fens. In the northern section and along upland areas belts of raised beaches, resulting of isostatic, postglacial rebound are prominent. To the southwest and south the region is bounded by Archean crystalline bedrock covered by calcareous loamy till and clayey lacustrine deposits. Moderate to high ice content permafrost is widespread, especially in organic deposits and along the northern boundary. Organic Cryosols and Mesisols are the dominant soils developed on organic materials, whereas Eutric Brunisols are associated with marine and till upland deposits. Wildlife characteristic of the region includes barren-ground caribou, snowshoe hare, willow ptarmigan, snow and Canada goose, and shorebirds. Human activities, while limited, include mining, hunting, trapping, sport fishing, and localized tourism. Shamattawa is the principal community and the population of the ecoregion is approximately 1200.
This ecoregion is part of the Hudson Plains ecozone.