It's a good question. When I boated on lake Erie there was a phenomenon called a "seiche". A sort of sloshing, like in a big bowl, that is caused usually by the wind but other factors can also cause it such as earthquakes, etc. A strong wind blowing for a long while can set up a seiche. I have seen Lake Erie change as much as 6 feet, flooding towns and causing beach erosion. On the other side of the lake the water is equally low.
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