where do the great lakes get their water
Great Lakes In 2009, the lakes contained 84% of the surface freshwater of North America;[40] if the water were evenly distributed over the entire continent's land area, it would reach a depth of 1.5 meters (5 feet).[15] The source of water levels in the lakes is tied to what was left by melting glaciers when the lakes took their present form. Annually, only about 1% is "new" water originating from rivers, precipitation, and groundwater springs that drain into the lakes. Historically, evaporation has been balanced by drainage, making the level of the lakes constant.[15] While the lake levels have been preserved, intensive human population growth only began in the region in the 20th century and continues today.[15] At least two human water use activities have been identified as having the potential to affect the lakes' levels: diversion (the transfer of water to other watersheds) and consumption (substantially done today by the use of lake water to power and cool electric generation plants, resulting in evaporation).[41]