Lake Winnipeg is a very large, relatively shallow 24,514-square-kilometre (9,465 sq mi) lake in North America, in the province of Manitoba, Canada. Its southern end is about 55 kilometres (34 mi) north of the city of Winnipeg. Lake Winnipeg is Canada's sixth-largest freshwater lake and the third-largest freshwater lake contained entirely within Canada, but it is relatively shallow excluding a narrow 36 m (118 ft) deep channel between the northern and southern basins. It is the eleventh-largest freshwater lake on Earth. The lake's east side has pristine boreal forests and rivers that were in 2018 inscribed as Pimachiowin Aki, a UNESCO World Heritage Site. The lake is 416 km (258 mi) from north to south, with remote sandy beaches, large limestone cliffs, and many bat caves in some areas. Manitoba Hydro uses the lake as one of the largest reservoirs in the world. There are many islands, most of them undeveloped.

The Nelson River is a river of north-central North America, in the Canadian province of Manitoba. The river drains Lake Winnipeg and runs 644 kilometres (400 mi) before it ends in Hudson Bay. Its full length is 2,575 kilometres (1,600 mi), it has mean discharge of 2,370 cubic metres per second (84,000 cu ft/s), and has a drainage basin of 1,072,300 square kilometres (414,000 sq mi), of which 180,000 square kilometres (69,000 sq mi) is in the United States.