Facts
Facts about Lake Winnipeg:
How big is Lake Winnipeg?
Lake size can be described in different ways. Perhaps the comparison most frequently encountered is by surface area. Different publications give slightly different figures for the surface area of Lake Winnipeg. The Government of Manitoba “Quick facts” web page gives its surface area as 23,750 square km, a figure that excludes the area of numerous islands in the lake. The Atlas of Canada gives the larger area of 24,387 square km as the “total area” which includes the islands. Regardless of the exact surface area, it is a very large lake. Inspection of a map of Manitoba reveals it as the dominant geographic feature of the province. It is often cited as the tenth largest freshwater lake in the world. The Wikipedia encyclopedia includes the Caspian Sea in a list of large lakes and ranks Lake Winnipeg as the 11th largest by surface area; if the Caspian Sea is excluded, Lake Winnipeg moves up to 10th rank. Lake Winnipegosis, another large lake just west of Lake Winnipeg, ranks 27th. Surface areas for some other large North American lakes are: Lake Superior 82,100 sq km, Lake Huron 59,500, Lake Michigan 57,750, Great Bear 31,326, Great Slave 28,568, Lake Erie 25,657, Lake Ontario 19,000.
The lake consists of three distinct regions, the smaller South Basin, the larger North Basin, and the “Narrows” connecting them.
Another way to describe lake size is by the linear distances across the lake in different directions. When measured along its north/south long axis, Lake Winnipeg is about 436 km long. At its widest point it is about and 111 km wide. The long length of the lake means that there are significant variations from one part of the lake to another.
Still another way to describe a lake’s size is by the volume of water it contains. This often varies seasonally because it depends on weather and river flows. Lake Winnipeg is shallow and consequently contains less water than many other large lakes. On average, Lake Winnipeg is only about 12 m deep although its deepest point is about 36 m. Estimates of the volume of water in it range from 284 cubic km (Manitoba Government ”Quick Facts” web page) to 371 cubic km of water (Kalff 2002). While these are huge volumes by most familiar measures, they are much smaller than many other large lakes. For example, volumes of some other large lakes in North America are: Lake Superior, 12,230 cubic km; Lake Michigan, 4,940 cubic km; Lake Huron, 3,537; Lake Erie, 483 cubic km, and Lake Ontario 1,637 cubic km (Kalff, 2002).
How big is the watershed that drains into Lake Winnipeg?
The watershed draining to Lake Winnipeg is huge, estimated to be nearly 1 million square km. It extends from near Lake Superior in the east, from west of Banff in the west, and from northern South Dakota in the south. Its drainage is about 40 times larger than its surface, a ratio bigger than any other large lake in the world. It drains large areas of northwestern Ontario, Manitoba, Saskatchewan, Alberta, North Dakota and Minnesota and small areas of Montana and South Dakota. It contains several internal drainage basins, areas that do not normally discharge to the rivers flowing to the lake but can sometimes do so in high-water seasons. Given the massive watershed and the relatively small volume of water in the lake, it is dominated by events in its watershed. It is not surprising to find it showing the effects of materials being added to it as a result of activities in the watershed.
Where does the water in the lake come from?
Water is supplied to the lake by three major river systems, the Winnipeg River from the east, the Saskatchewan River from the west and the Red River from the South, by direct inputs of rain and snow to the surface and by several smaller rivers. In earlier times the Saskatchewan River was the largest inflow of water but in recent times the flow of that river has declined while flows in the Winnipeg and Red Rivers have increased with the result that the Winnipeg River has become the largest single source. The Winnipeg River drains mainly Precambrian shield area to the east of the lake while the Saskatchewan River arises in the Rocky Mountains and flows through mostly prairie soils. The Red River drains prairie soils for its whole length. The lake has only one outflow namely the Nelson River which carries water north and east through several smaller lakes on its way to Hudson Bay.
How long does the water stay in the lake?
The inflows of the rivers, and direct precipitation to the surface, combined with the relatively small volume of the lake, give it a comparatively short water residence time of less than one year for the South Basin and about three to four years for the lake as a whole. The water residence time is the theoretical time that would be required to fill the lake up again if all of its water were suddenly removed from it. Freshwater lakes have highly variable water residence times ranging from a few days to thousands of years. The lake with the longest water residence time is Lake Tanganyika in Africa with a water residence time of 6000 years. The water residence times for some other large North American lakes are: Lake Superior 191 years, Great Bear Lake 131 years, Lake Michigan 99 years, Lake Huron 22 years, Lake Ontario 6 years, Lake Erie 2.6 years.
What is the history of the lake?
Northern North America has been covered with glaciers several times and the most recent glacier began to retreat from the area now occupied by Lake Winnipeg about 12,000 years ago. Glacial melt water accumulated at the receding edge of the glacier and formed a huge lake, called Lake Agassiz. The shape and size of Lake Agassiz changed dramatically over time as the glacier receded and as water in the lake drained out from time to time through several channels. The ice was originally up to 4 km thick and it retreated over several thousand years leaving the present-day remnant we know as Lake Winnipeg. The weight of the ice deformed the planet’s crust and it is rebounding upwards very slowly. The northern end of the lake is rebounding faster than the southern part so that the lake is slowly tilting slightly toward the south. As a result, water levels in the south are increasing slowly – at about 20 cm per century - but still enough to raise concerns about erosion of shorelines.
What is the history of human settlement around the lake?
Following the ebb and flow of glaciation, permanent human habitation commenced approximately 8,000 years ago with the ancestral beginnings of the Cree and Ojibway cultures. With water as the source of life, Lake Winnipeg and its tributaries were a dominant influence both in their world view and daily life. Seasonal rhythms would see extended groups come together near the mouths of the rivers at the edge of the lake for summers of fishing, harvesting of rice as well as visiting and celebrations. Many of these groups then followed the great herds of bison to the open prairie in the fall; then they would break into smaller, more sustainable family groups to move inland along the rivers to the Boreal forests for winter. The tempestuous big lake was probably not often traversed by the birch bark canoes of the First Nations, who paddled along its shores thereby becoming intimately familiar with its varied resources and landscapes. Fish and wildlife enriched the diet and provided skins and tools from their seasonal travels, while a sophisticated trade network developed to provide a broader range of material culture, including metal for tools, seeds for cultivation and ideas for technological innovation. The name ‘Lake Winnipeg’ is a gift from ancient times that means ‘murky water’, a reference to the turbid habits of the great lake. It was the abundance of fish in these murky but verdant waters that also lured European habitation in the post-contact period. Early settlement along the shores include fur trade provisioning posts, Métis fishing camps, Icelandic settlers along the west shore and ultimately, summer residences facilitated by the coming of the railway on both sides on the south basin in the early twentieth century.
Lake Winnipeg as a hydro-electric reservoir
The water level in Lake Winnipeg is usually from about 711 to 715 feet above that in Hudson Bay. That is, water leaving Lake Winnipeg via the Nelson River falls over 700 feet on its journey to Hudson Bay. That flow of water offers opportunities to generate hydro-electricity and Manitoba decided during the 1960s to exploit that potential using a series of generating stations along the Nelson River. In order to ensure that sufficient water flow was available in the Nelson River, especially in winter when the demand for power is high, a number of dams and diversions were built. With the construction of the Jenpeg dam on the western arm of the Nelson River where it flows into Cross Lake, the levels of water in the lake could be regulated and water could be allowed to flow out of the lake as it was needed by the generating stations. Several generating stations have been built and others are in various stages of planning.
Recreational use of the lake
Lake Winnipeg has numerous excellent recreational beaches and these have provided summer recreation for hundreds of thousands of people for decades. The most popular beaches are on the South Basin because they are closer to where most Manitobans live. Excellent beaches are also found in the North Basin but access to them is more limited. The most popular beach is at Grand Beach Provincial Park on the east side of the lake. This area regularly attracts over half a million visitors per year. Tourism of various kinds is a big industry with thousands of cottages (increasingly being converted to year-round use), recreational fishers, boaters, naturalists, campers, and others.
Lake Winnipeg supports a vibrant commercial fishing industry. A News Release by the Government of Manitoba (June 25, 2010) cited a value of $50 million per year for the economic activity related to commercial fishing. Some 3000 workers are involved in the industry from catching the fish to processing them for market. The principal commercial species are walleye, sauger and whitefish.
The lake is home to many more species than commercial fish including forage fish, invertebrate animals and various species of birds and other wildlife.
Problems facing the lake
Chemical
The most immediate problems are the algal blooms that cover large areas of the lake late in the summer and in the fall. About 8 000 tonnes of phosphorus enter the lake each year but only a small fraction of that actually leaves the lake and flows down the Nelson system. This phosphorus is available to the algae in the lake and when conditions of warm water and low winds apply, they can form huge blooms easily visible in satellite images. The dominant organisms in these blooms are blue-green types of algae, classified scientifically as specialized types of bacteria called Cyanobacteria. These organisms can produce highly toxic compounds similar in structure to very small proteins and so they represent more than an unsightly nuisance. When these algae die, decomposition of them takes oxygen out of the water and can reduce the oxygen so much that fish and other animal life can suffocate. This problem of excess algae, called “eutrophication” is a world-wide problem in lakes in populated areas. There is good evidence that the root cause behind the problem lies with the amount of the element phosphorus in the lakes. That is, the amount of phosphorus in a lake limits the amount of algae that can grow there because they need phosphorus and cannot make it themselves. The only solution found so far is to cut back on the phosphorus entering the lakes.
Biological
Reports from the 1930s described blooms of algae in Lake Winnipeg and so the lake has produced blooms even before it received large quantities of phosphorus from its watershed. Satellite pictures of the lake reveal that the size and frequency of blooms have been increasing in recent years. 
The two main limitations on the production of these algae are the amount of phosphorus and the amount of light. Algae, like green plants, need both food and light. These algae need other chemical elements too but the other main nutrient element, nitrogen, is one they can make for themselves from nitrogen gas in the air. (Air is about 80 % nitrogen). The South Basin of the lake is normally quite turbid due to inflows of soil particles mainly from the Red River. Light cannot penetrate turbid water very deeply and that limits algal growth there. The North Basin has clearer water with more penetration of light and the algae bloom there more regularly.
The other biological problems relate to invasions of the lake by new species (such as the rainbow smelt) and anticipated arrivals of other unwanted species (zebra mussels). Also, several species have been placed on lists of species that are ”rare” or “at risk” of being lost from the lake.
Physical
Manitoba Hydro creates hundreds of millions of dollars in electrical power each year by regulating water flows, largely on the Nelson River, including those from Lake Winnipeg, and passing the water through generating stations. This industry massively changes the flow of the rivers so that the maximum discharge is in winter when power demand is high rather than in summer which is the natural seasonal pattern of maximum discharge. The regulation of water levels in the lake has brought into question the stability of shorelines to erosion.
Manitoba has been subject to flooding, especially in the Lake Winnipeg drainage, for centuries and probably for millenia. Efforts to get rid of water quickly to facilitate agricultural production have resulted in the drainage of about 70 per cent of our natural wetlands and the creation of a network of drainage canals. These activities deliver water efficiently to the lake but also deliver loads of phosphorus and other chemicals.
Political
Lake Winnipeg’s drainage basin falls into jurisdictions of two national governments, four provincial governments, two state governments and many more municipal and First Nations governments.
Reaching agreeable solutions is difficult when so many jurisdictions are involved especially when benefits in one area may invoke costs in another.