The largest Freshwater lake is

Lake Superior:- It is the world's largest freshwater lake by surface area and third-largest by volume.  It holds 10% of the world's fresh water on the surface. 

It is bordered on one side by Ontario, Canada, and on the other by states in the United States: Minnesota to the west, and Wisconsin and Michigan's Upper Peninsula to the south.  The Great Lakes chain's most northerly and westerly lakes, as well as the highest in height, are Lake Superior and Lake Michigan.  The St. Mary's River drains into Lake Huron.

Final Answer: Hence, the correct option is (a) i.e. Lake Superior