Glacial Lake Wisconsin formed near the end of the last glacial period, about 18,000 to 14,000 years ago, when a lobe of the continental glacier blocked the normal flow of the Wisconsin River. Meltwater backed up against the ice and surrounding hills, creating a broad lake that spread across much of central Wisconsin. The lake’s life was brief. Around 14,000 years ago, the ice dam failed, releasing the water in a sudden outburst flood. Instead of slowly eroding the landscape, this surge tore thro