What is Lake Winnipeg?

Lake Winnipeg is the largest lake in Manitoba and the eleventh-largest freshwater lake in the world by surface area at 24,514 square kilometres. The lake is shallow (mean depth about 12 metres, maximum depth 36 metres) and elongated, stretching about 425 kilometres north to south but only 100 kilometres east to west at its widest. Lake Winnipeg sits on the boundary between the prairie region of southern Manitoba and the Canadian Shield to the east and north.

The lake drains an enormous watershed of about 980,000 square kilometres including parts of Manitoba, Saskatchewan, Alberta, Ontario, Minnesota, North Dakota, South Dakota, and Montana. Major rivers feeding the lake include the Red River from the south (which originates in North Dakota and flows north through Winnipeg), the Saskatchewan River from the west (which drains most of the prairie provinces), the Winnipeg River from the east (which drains Lake of the Woods and the western Ontario Shield), and the Bloodvein, Berens, and Poplar Rivers from the east (which drain the eastern Manitoba Shield). The lake itself drains north via the Nelson River about 644 kilometres to Hudson Bay.

Lake Winnipeg is one of Canada's most productive freshwater fisheries, with major commercial catches of walleye (called pickerel locally), sauger, lake whitefish, goldeye, and yellow perch. The Lake Winnipeg lake whitefish fishery has been certified by the Marine Stewardship Council. Indigenous fisheries on the lake have operated for thousands of years and continue under modern co-management arrangements with the Manitoba government and federal Department of Fisheries and Oceans.

Lake Winnipeg has suffered significant water-quality problems since the 1990s. Excess phosphorus from agricultural runoff (particularly from the Red River basin in North Dakota and Minnesota), urban wastewater (including untreated combined sewer overflows from Winnipeg), and livestock operations has fuelled annual cyanobacterial (blue-green algae) blooms that cover up to 15,000 square kilometres of the lake's north basin. The federal Lake Winnipeg Basin Initiative (since 2007), the Manitoba Phosphorus Reduction Strategy, and the international Red River Basin Commission coordinate response. Climate change, invasive zebra mussels (first detected in 2013), and lake-level regulation by Manitoba Hydro for the Nelson River hydroelectric system are additional challenges. The eastern shore of Lake Winnipeg is protected within Pimachiowin Aki, a UNESCO World Heritage Site since 2018 and the world's largest contiguous boreal forest protected area led by Indigenous nations.