Photo:  Weather Underground

By Tanda Gmiter - [email protected] - October 3, 2017

CALUMET, MI - Sometimes it's hard to get your head around the vastness that is Lake Superior.

The largest of our Great Lakes, the behemoth carved by glaciers acts more like an inland sea. And it's just as deadly, its bottom littered with thousands of shipwrecks.

Maybe this will help put its size and movements in perspective: A drop of water that fell into Lake Superior in October, 1826 has finally reached the St. Mary's River this month. It's now headed to Lake Huron.

And after a total journey adding up to a couple centuries, it will become part of the Atlantic Ocean.

How do researchers know this? Have they been tracking a tiny raindrop since the summer Thomas Jefferson died?

Of course not. This fun factoid was shared earlier this year by the Keweenaw National Historical Park, a heritage site in Calumet, in Michigan's Upper Peninsula.

Staff there used the example to explain how long water remains in Lake Superior. Its water retention/replacement rate is 191 years, by far the longest in the Great Lakes system.

A later study pegged the retention time at closer to 173 years, but it's still a big number.

The national park was using the retention time to alert people that while Superior is a giant, it's also fragile. Pollution that dissolves in its waters stays there.

By comparison, water stays in Lake Michigan for about 62 years, Lake Huron for 21 years, and Lake Erie for less than three years