There was a very interesting show on one of the Discovery channels, or National Geographic last month. They said the Great Lakes are less than 15,000 years old, and the bottoms of the lakes are actually rising more than 1/2" per year now that the weight of the glaciers is off of them. As the bottom rises, the water quantity in them gets smaller, and there is even less weight on the bottoms, so the lake bottoms rise even faster. Additionally, the mouth of the Niagra River at the falls recedes 3' per year due to erosion, and in 1000 years the mouth of it will be at the shore of the "big lake" and will actually drain all of the Great Lakes. Pretty interesting show...glad I won't be around to see Lake St Clair turn into a swamp.