The Hudson Bay has the longest shoreline of any bay in North America and indents deeply into east-central Canada. It is bounded by the territory of Nunavut in the north and west; Manitoba and Ontario in the south and Quebec in the east. In the northeast, it is connected with the Atlantic Ocean through the Hudson Strait; while in the north, it is connected with the Arctic Ocean through the Foxe Channel and the Fury and Hecla Strait. James Bay is the southern extension of the Hudson Bay, situated between northern Ontario and Quebec.
The bay lies in a large saucer-shaped basin and occupies the southernmost part of the marsh-ridden Hudson Bay Lowlands, which is fed by the lake waters and numerous turbulent rivers. The large drainage basin of the Hudson Bay includes parts of the Canadian provinces of Manitoba, Ontario, Quebec, Alberta, and Saskatchewan; the Canadian territories of Northwest Territories and Nunavut; and some smaller parts of the US states of Montana, Minnesota, North Dakota and South Dakota.