 The retreat of the ice sheet left behind a large amount of meltwater (see Lake Algonquin, Lake Chicago, Glacial Lake Iroquois, and Champlain Sea) that filled up the basins that the glaciers had carved, thus creating the Great Lakes as we know them today.Scientists argue there is an old valley, St David's Buried Gorge, buried by glacial drift, at the approximate location of the present Welland Canal.When the ice melted, the upper Great Lakes emptied into the Niagara River, which followed the rearranged topography across the Niagara Escarpment.