The Great Lakes—Huron, Ontario, Michigan, Erie, and Superior—are five blue jewels set a bit off center in a belt across North America’s middle. Bordered by eight states and part of Canada, the Lakes hold 21% of the world's fresh water. How did these incredible lakes get there? And what can we do to preserve such a treasure? Follow along as a drop of water in this enormous system and uncover its dramatic journey from lake to rive to lake, over Niagara Falls to lake and river again, and finally into the Atlantic Ocean.