This ecoregion extends west from James Bay in Quebec to Attawapiskat River in northern Ontario. It is marked by cool, short summers and cold winters. The mean annual temperature is approximately -2°C. The mean summer temperature is 11.5°C and the mean winter temperature is -16°C. The mean annual precipitation ranges 700-800 mm. The ecoregion has a perhumid high boreal ecoclimate. It is an area of transition, lying between the coniferous and mixed forests of the clay belt to the south, and the tundra to the north. In the southern section and along rivers, the forests are composed of balsam fir, white and black spruce, trembling aspen, and paper birch. Most of the ecoregion is poorly drained, and the dominant vegetation consists of sedge, mosses, and lichens with or without stunted black spruce and tamarack. The ecoregion is underlain by flat-lying, Palaeozoic limestone bedrock of the Hudson Bay Lowland. These lowlands slope gently towards James Bay. Most of the Quebec section of the ecoregion is part of the Eastmain Lowland. The ecoregion consists largely of flat, poorly drained plains with subdued fluvial and marine features. Throughout the area, there are gravelly, well-drained belts of raised beaches, resulting from postglacial, isostatic rebound. To the south, the region is dominated by fine-textured lacustrine and marine deposits. Wetlands cover between 50% of the area in the south to over 75% of the area in the north and around James Bay. They are composed largely of northern ribbed fens, northern plateau bogs, and palsa bogs. The soils are dominantly Organic Mesisols and Fibrisols with some Organic Cryosols. Limited areas of Dystric and Eutric Brunisolic soils occur on upland sands. Eutric Brunisols and Gleysols are associated with river levees, while clayey uplands may have Gray Luvisol soils. Sporadic, discontinuous permafrost with medium to high ice content in the north decreases to isolated patches surrounding James Bay. Mineral soil profiles exhibit uneven and often discontinuous or distorted soil horizon development as a result of past and present permafrost action. Characteristic wildlife includes barren-ground caribou, black bear, wolf, moose, lynx, and snowshoe hare. Bird species include the Canada goose, ruffed grouse, and American black duck. Land use activities include tourism and recreation, hunting, trapping, and fishing. The major communities include Attawapiskat, Eastmain, Waskaganish, and Moosonee. The population of the ecoregion is approximately 7100.
This ecoregion is part of the Hudson Plains ecozone.