The waters of the Great Lakes are, for the most part, a nonrenewable resource. They are composed of numerous aquifers (groundwater) that have filled with water over the centuries, waters that flow in the tributaries of the Great Lakes, and waters that fill the lakes themselves. Although the total volume in the lakes is vast, on average less than 1 percent of the waters of the Great Lakes is renewed annually by precipitation, surface water runoff, and inflow from groundwater sources.
A diversion is any transfer of water across watershed boundaries through a man-made pipeline or canal. Diversions may transfer water in or out of the Great Lakes basin, or between the watersheds of different lakes or rivers within the basin. While the impacts of existing diversions on lake levels are minor, they alter the natural flow of the Great Lakes and water returned from diversions may be of a different quality than when it was withdrawn.
The Dynamic Great Lakes click the link for more information about interconnected Great Lakes system.