Lake Superior Contains 10% of all of the Earth’s (non-frozen) freshwater. It is the largest freshwater lake on the planet, and is only 10,000 years old. Average summer temperature there is only 40ºF.
How did it form, and why is it so cold?
During the last ice age, the ice was 2km thick over the region. The moving ice carved and depressed the land, and when the ice melted the Superior Basin filled up with ice water. The water has warmed slowly over the last 10,000 years and still remains quite cold.
No doubt governments were very upset at the rapid rate of ice loss and sea level rise 10,000 years ago. Yet there really wasn’t anything they could do about it.
Fortunately, we have returned to a milder climate where people don’t have to wear those thick Mastodon coats any more.