Covering approximately 295,000 miles[11] between eight states and one Canadian province, the Great Lakes-St. Lawrence River system includes Lakes Superior, Michigan, Huron[12], Erie and Ontario and their connecting channels.
Graphic courtesy of the U.S. Department of the Interior.

The hydrograph above depicts water levels for Lake Michigan-Huron over the past 5,000 years, from 3,000 BC to the present. The upper x-axis refers to the entire 5,000-year cycle measured, while the lower x-axis refers to actual calendar years. The y-axis at left measures water levels in meters, and in feet at right.
Graphic courtesy of the U.S. Department of the Interior.

This “strandplain” near Manistique, Mich., illustrates the variability of water levels. The series of ridges that comprise the strandplain were produced by the deposit of sand by waves. Higher lake levels deposited sand farther inland.

Shorelines quickly adapt to the rise and fall of water levels, as the photos above illustrate. Photo 1 (upper left) shows a patch of wetland along the Pigeon River near Sheldon, Mich., when water levels dropped more than 1.5 feet from the previous year. Photo 2 (upper right) shows the same patch one year later, when annual emergent plants grew from the seed bank. Photo 3 (lower left), from 2001, displays the perennial emergent plants that displaced annuals along the shore. Photo 4 (lower right), from 2003, shows the shift to a different perennial plant community.