[originally appeared on The Earth Story]
In any map of North America, the Great Lakes draw the eye to their irregular shape, stamped on the continent like an aquatic Rorschach test. Formed after the last glacial period, the five lakes straddle the border between the US and Canada and contain centuries of history in their shipwreck-studded depths. Erie, Ontario, Huron and Michigan, and the largest of them all, Superior, together make up the largest system of fresh surface water in the world, providing drinking water for 40 million people around their shores and generating billions of dollars in revenue from tourism and recreational or commercial boating and fishing.
(Courtesy NASA https://visibleearth.nasa.gov/view.php?id=78617)