As the ice retreated, Lake Superior's present outlet was established through the St. Marys River, and the water level fell. That's ten percent of the world's fresh surface water and over half of the water in the Great Lakes. Lake Superior contains enough water to submerge all of North and South America under one foot of water. That's about 28 times the flow of the St. Louis River as it enters Lake Superior. Tidal motion, caused by the gravitational pull of the sun and moon is negligible in all lakes, including Lake Superior.
Seiches occur after water is piled up on one side of the lake by wind or high barometric pressure.
When this force shifts or diminishes, the water rocks back and forth from one shore to the other with decreasing amplitude, like water in a pan that's been tipped then laid flat. The effect is strongest when the wind blows off the water, and is most pronounced on the shore and on slopes that face the lake. Between late spring and late fall, the shore can be shrouded in fog when inland areas bask in sunshine. These warm-season fogs occur when moisture in the warm air condenses as it flows over the cold lake. These foggy days, punctuated with the sounds of gulls and fog horns, have a powerful appeal.