Lake Winnipeg is located in central Canada in the Province of Manitoba. With a total area of 24,400 sq. km it is the 10th largest freshwater lake in the world. The 416 km long lake is separated into two basins, a larger northern area about 100 km wide and a smaller 40 km wide southern basin. Both basins are connected through a 2.5 km-wide channel called The Narrows. The average depth of Lake Winnipeg is 12.0 m with 13.3 m and 9.7 m in the North and South basins, respectively. This freshwater lake lies at an altitude of 218 m asl.
Lake Winnipeg is the largest remnant of the giant prehistoric Lake Agassiz that formed as deglaciation proceeded between 12,000 and 8,000 years ago. Lake Winnipeg assumed its present shape about 2,500 years ago when independent northern and southern basins coalesced as the underlying land rose with removal of the ice sheet load.
Lake Winnipeg and its main rivers are highly regulated for hydro power production. Three inflows, the Red, Saskatchewan, and Winnipeg Rivers, deliver more than 70 % of the water to the lake while a sole outlet, the Nelson River, flows into Hudson Bay.
In 1976, Lake Winnipeg became the world’s 3rd largest hydro reservoir when the Jenpeg Dam was constructed on the Nelson outflow to regulate lake levels. About 65 % of water entering Lake Winnipeg passes through several power plants on the Winnipeg and Saskatchewan Rivers. Electric power is exported to adjacent provinces and states and provides important revenue for the provincial economy.
Besides hydroelectric energy production, the lake sustains a large commercial and traditional fishery reliant on Walleye (Sander vitreus), Sauger (Sander canadensis), and Whitefish (Coregonus clupeaformis). Recent Lake Winnipeg walleye yields have surpassed those of Lake Erie, the previous top producer in North America. Three fish species were introduced to the lake: Rainbow Smelt (Osmerus mordax), Common Carp (Cyprinus carpio) and White Bass (Morone chrysops). Their impacts on native fish populations are not known.
Agriculture is the predominant economic activity throughout the vast (1,000,000 sq. km). Lake Winnipeg watershed and the main contributor of nutrients to the lake. Additional landscape modifications such as wetland, forest and native vegetation loss, artificial drainage, and hard urban surfacing have exacerbated nutrient and contaminant loading to the lake with a resulting shift in algal species composition to nuisance, toxic algal strains which imperil lake food web function as well as human health.
During summer months, enormous algae carpets are now commonly found floating on the lake or dumped along shore lines. The increased risk from algal toxins and E. coli has subsequently led to more frequent closures of several popular Lake Winnipeg beaches.
Since 2002, more research and attention has been paid to the health of Lake Winnipeg. Through the efforts of groups like the Lake Winnipeg Research Consortium and the Lake Winnipeg Foundation, government and university research on this complex lake is underway and public awareness of the problem has increased. New emerging threats such as climate change, invasive species, and chemical contaminants will require continuing vigilance and care from all who depend on Lake Winnipeg for their livelihood or enjoyment.