Prior to the beginning of the ice age about 2 million years ago, the present Great Lake area was occupied by a river drainage system that emptied into the area of Hudson's bay.The current pattern of the Great Lakes mimics that of this ancient river system because the glaciers moved into the valleys from the north and greatly deepened them to form basins which were then filled with meltwaters when they retreated 10,000 years ago.
Sediment from land areas is gradually being carried into these basins, by wind, water currents, and people. It will continue to do so until the Great Lakes are eventually filled up and are no more.
