North America is generally considered to include Central America, south to Panama. North America is entirely within the northern hemisphere. It has the largest fresh-water lake in the world, Lake Superior, one of the Great Lakes. Four of the five lakes serve as the border between the United States and Canada. (Lake Superior, Lake Eerie, Lake Huron and Lake Ontario, while Lake Michigan is solely within the US). The Mississippi/Missouri river system is the longest in the world, and is almost entirely within the United States. North America, north of Central America, is dominated by three large countries - Canada, United States and Mexico - each of which stretches all the way across the continent, from the Atlantic Ocean to the Pacific.