What is the largest freshwater lake by surface area?

The largest freshwater lake by surface area is Lake Superior.

Lake Superior covers about 31,700 square miles (82,100 square kilometres), making it the largest freshwater lake on Earth when measured by surface area. It lies between Ontario, Canada, and Minnesota, Wisconsin, and Michigan in the United States, and is the northernmost and westernmost of North America's Great Lakes.

The lake was shaped largely by glaciers during the last Ice Age. Its enormous basin holds roughly 12,100 cubic kilometres of water—enough to cover North and South America with about 30 centimetres of water. Despite its size, Superior drains through the St. Marys River into Lake Huron and ultimately the Atlantic Ocean.

A common mix-up is the Caspian Sea, which is larger but saline rather than freshwater. Lake Baikal contains more freshwater by volume, while Lake Tanganyika is deeper and longer. Lake Michigan and Lake Huron are sometimes treated as one hydrological lake, but as separately named lakes, neither exceeds Superior in surface area.