Lake Winnipeg (52°N, 92°W) is a large (24 400 km²) lake in central North America, in the province of Manitoba, Canada, at about 55 km north of the city of Winnipeg.

It is the sixth-largest freshwater lake in Canada, exceeding even Lake Ontario in size, but it is relatively shallow (maximum depth 18m). It is elongated in shape, 416 km from north to south.

The lake's watershed measures about 984 200 km², and covers much of Alberta, Saskatchewan, Manitoba, northwestern Ontario, Minnesota, and North Dakota. Some of its tributaries include:

• the Saskatchewan River (through Cedar Lake),
• the Red River (draining the Assiniboine River),
• the Winnipeg River (draining Lake of the Woods, Rainy River and Rainy Lake ); and
• Lake Manitoba (draining Lake Winnipegosis).

Lake Winnipeg drains northward into the Nelson River at an average annual rate of 2066 m³/s, and forms part of the Hudson Bay watershed.

Lakes Winnipeg, Manitoba, and Winnipegosis are found at the floor of the prehistoric Glacial Lake Agassiz. The area between Lake Winnipeg and Lakes Winnipegosis and Manitoba is called the Interlake Region, and the whole region is called the Manitoba Lowlands.

The first European to have seen the lake is believed to have been Henry Kelsey in 1690. He adopted the Cree language name for the lake: wīnipēk (ᐐᓂᐯᐠ), meaning "muddy waters". Later, the Red River Colony to its south would take the lake's name and become Winnipeg, the capital of Manitoba.

Due to its long, narrow shape, the lake exhibits a variety of interesting wind and wave effects, including waves of up to one metre in height at its southern shore, a process called wind tide . This occurs 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. 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 flood 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 .

Communities on the lake include Riverton , Gimli, Winnipeg Beach , Victoria Beach , Pine Falls , Manigotagan , Berens River , and Grand Rapids . A number of pleasure beaches are found on the southern end of the lake.

Lake Winnipeg serves as an important commercial fisheries, shipping route and the southern shore is a popular summer resort area.