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Hudson Bay

Although technically, the Hudson Bay watershed is part of the Arctic Ocean watershed, it is often studied as its own system. The largest ocean watershed in Canada, with an area of about 3.9 million square kilometres, the Hudson Bay watershed includes Hudson Bay, James Bay, Ungava Bay and Foxe Basin. It captures 30 percent of the water runoff in Canada, and the rivers that flow into Hudson Bay and James Bay make up 20 percent of the freshwater flow into the Arctic Ocean. The Nelson River and Manitoba's Churchill River drain east from the Continental Divide toward Hudson Bay, flushing the bay with fresh water. Each year, James Bay receives enough fresh water to raise its water level by the equivalent of 4.73 metres.

Altogether, Foxe Basin, Hudson Bay and Hudson Strait create a large inland sea system in Canada that is characterized by the mixing of Arctic marine seawater coming in from the North and vast amounts of freshwater runoff flowing in from terrestrial river systems.

The fresh water and nutrients that flow from the land to the sea in this ocean watershed support rich estuaries and marine ecosystems. In the late 1980s, the Nelson River Estuary boasted the largest single concentration of beluga whales in the world, and the salt marshes and eelgrass beds that thrive in this estuarine environment support vital concentrations of migratory birds.