The lake lies in a lowland basin that was scoured out of the limestone and shale bedrock by continental glaciers during the ice ages. When the glaciers finally melted, about 12 000 years ago, a large lake, Glacial Lake AGASSIZ, filled the entire basin. It gradually drained and exposed a flat plain that extends from the Manitoba Escarpment in the west to the rocky edge of the Precambrian Shield in the east. Today the glacial lake bottom constitutes the Manitoba Lowlands and is occupied by lakes Winnipeg, WINNIPEGOSIS and MANITOBA.
English explorer Henry KELSEY (1690) may have been the first European to see the "murky waters" (win-nipi) and adopted this Cree Indian name for the vast freshwater body. The lake soon became an important transport link between the Hudson Bay port of York Factory and the fur-trade hinterlands of the Red-Assiniboine watershed. In 1812 Lord Selkirk's boats traversed the length of Lake Winnipeg on their way to founding the RED RIVER COLONY at the junction of the Red and Assiniboine rivers. Later the lake gave its name to this community, which later became the capital of the new province of Manitoba.
On long and relatively narrow lakes such as Lake Winnipeg, interesting wind and wave effects occasionally take place. When prevailing northerly winds blow along the length of Lake Winnipeg, they exert a horizontal stress on its surface. Surface waters move in the direction of the wind and pile up along the windward south shores - a phenomenon known as a setup or wind tide. Setups greater than 1 m above normal lake levels have been recorded along many of southern Lake Winnipeg's recreational beaches, and the associated high waves with their uprush effects have caused considerable storm damage, backshore flooding and shoreline erosion. The highest setups occur in the fall, when the northerly winds are strongest. If the winds die down suddenly, the waters rush northward, then slosh back and forth in a process called seiching.
Author R.A. MCGINN
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Down on the Lakes of Manitoba
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