Lake Winnipeg watershed
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Water quality in Lake Winnipeg has deteriorated over time, as evidenced by the increasing frequency and intensity of algal blooms in the lake in recent years. Increased nutrient (phosphorous and nitrogen) loading to the lake from the Lake Winnipeg watershed is one of the key reasons for these algal blooms. While some scientific data had been collected on Lake Winnipeg over the years, much of the intensive monitoring on the lake has occurred since 1999. Knowledge of the structure and function of Lake Winnipeg has been advanced through intensive federal, provincial, joint, and independent research and monitoring programs. Research and monitoring programs have improved our understanding of the physical, chemical and biological characteristics of the lake and the sources and fate of nutrients transported to Lake Winnipeg. Until now, there has been no systematic attempt to summarize these data to establish a better understanding of the current state of the lake. To address this issue, Environment Canada and Manitoba Water Stewardship, along with many others conducting research and monitoring on the lake, have worked together to produce a State of the Lake report for Lake Winnipeg to summarize the current scientific knowledge on the lake, focusing on the period from 1999 to 2007. The report, which is available as both a highlights and extended technical document, is intended to serve as a baseline for future lake assessments and presents key information that will help to support the development of performance indicators and ecologically relevant nutrient objectives for Lake Winnipeg.
The Lake Winnipeg watershed extends from the Rocky Mountains to within a few kilometres of Lake Superior, and from the northern tip of the lake south to South Dakota. The watershed is the second largest in Canada and spans approximately one million square kilometres including parts of four Canadian provinces and four U.S. states. Of the roughly 7 million people in the watershed, nearly 80% live in large cities such as Calgary, Edmonton, Saskatoon, Regina, Winnipeg and Fargo. The watershed is dominated by agricultural land use, which has implications for the quantity and quality of water entering the lake. The western part of the watershed is predominantly cropland while forested areas dominate the eastern side of the lake in the Boreal Shield region.
The three major rivers feeding Lake Winnipeg are the Saskatchewan, Red (including the Assiniboine) and Winnipeg rivers. Hydrology within the watershed is highly regulated, with numerous dams and diversions, which alter the natural flow in rivers draining to Lake Winnipeg. Research has indicated that the abundant lakes and reservoirs upstream of Lake Winnipeg sequester nutrients, reducing their transport downstream. The size, geographical diversity, and the inter-jurisdictional and international nature of waters within the watershed present unique challenges to water resource management, including measures to reduce nutrient loading to Lake Winnipeg.
At 23 750 square kilometres in area, Lake Winnipeg is the tenth-largest freshwater lake in the world, and the sixth-largest lake in Canada. Lake Winnipeg consists of a large, deeper north basin, and a smaller, comparatively shallow south basin. Lake Winnipeg is shallow relative to other large lakes, with an average depth of 9 m in the south basin and 13.3 m in the north basin. The two basins are separated by the narrows through which waters from the south basin ultimately flow northward. The north and south basins differ not only in size and depth, but also in water quality and biological characteristics. The Nelson River is the only outlet from the lake, flowing northward to Hudson Bay. The outflow of the lake has been regulated for hydroelectric power generation since 1976, making Lake Winnipeg the third-largest hydroelectric reservoir in the world. The lake is of substantial socio-economic and cultural importance, supporting numerous shoreline communities and sustaining a variety of uses including fisheries, recreation and hydroelectric power, which are key components of the provincial economy.
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