Lake Manitoba is a large (4,624 sq.km.) lake in central North America, in the Canadian province of Manitoba. It is located about 75 km northwest of the province's capital, Winnipeg, at 51°N 98°45'W.

The irregularly shaped lake, about 200 km long, is the smallest of a group of three large lakes, the other two being Lake Winnipeg (the largest) and Lake Winnipegosis, which are found on the floor of the prehistoric Glacial Lake Agassiz. In the lake, there is a large island that has a lake in it, and in that lake, there are also a few islands!

It is primarily fed by Lake Winnipegosis to its northwest via the Waterhen River , and drains northeast into Lake Winnipeg via the Dauphin River . It is thus part of the watershed of the Nelson River and Hudson Bay.

The southern tip of the lake, 24 km north of Portage la Prairie, Manitoba, ends in the Delta Marsh, an important staging ground for migrating birds.

Communities on the lake include Fairford , Steep Rock , St. Laurent , and Amaranth .

The lake, its shores populated by the Assiniboine Cree , was made known to Europeans by La Vérendrye in the mid-1730s. It was part of the route of the fur trade to Hudson Bay.

The name derives from Cree manitou-wapow or Ojibwa manitou-bah, both meaning "straits of Manitou, the Great Spirit," a toponym referring to what are now called The Narrows in the centre of the lake. The lake was known to French explorers as Lac des Prairies.

For many years there have been claims that a monster similar to the Loch Ness Monster and Ogopogo lives in the lake. It has been named Manipogo .