During the most recent glacial period, glaciers slowly moved across the regions now known as minnesota and wisconsin, carving up and deepening ancient valleys. when the glacial period ended, what most likely happened to these deep valleys
Most of the deep carvings left in this region following the last glacial period have now turned into lakes and streams. Prior to these existing, it is believed that the water that accumulated in the area washed off to the ocean now a more extensive water way has been created, keeping more water in the area.