Lake Superior is the largest body of fresh water with a surface area of about 82,103 square Km, however Baikal in Siberia has a greater volume of water. Lake Baikal holds 5,700 cu mi, while Lake Superior holds 2,800 cu mi. Baikal is also the world's most ancient freshwater lake, it originated 20-25 million years ago. It is home to many unique species of animals and plants including the freshwater seal. Lake Baikal is one of the clearest and purest bodies of water.

Thus while a few lakes, such as Lake Superior would appear to be larger from a bird's eye view, Lake Baikal in fact holds more fresh water than any other lake in the world. Lake Baikal has a depth of 1, 642m, while Lake Superior has a depth of 406m. Looks can be deceiving.

More Info: en.wikipedia.org