In 2002, the Great Lakes basin had just 11.9% ice coverage, NOAA said. In 2012, Lake Superior had 8.5% coverage. In 2002, Lake Michigan had 12.4% coverage.

The process forming the Great Lakes began millions of years ago but wasn't completed until the last ice age, 20,000 years ago. The northern shore of Lake Superior, Ontario, Canada.

As of March 16, average ice cover across the lakes was roughly 13.5%. Lake Superior was at 9.2%, and Lake Michigan was at 10.7%.