About Lake Michigan

The Great Lakes are relatively young, having formed only in the last 10,000 years. During the Pleistocene epoch, glaciers 6,000 feet thick advanced and receded several times over the Great Lakes region. Large volumes of water melted from the glaciers as they retreated, filling the scoured depressions. Uplift of the land, as the weight of the glaciers was removed, caused changes in the depth and drainage patterns of the area. The Great Lakes as a whole contain the largest volume of freshwater in the world. Lake Superior is the largest freshwater lake by surface area but is exceed in volume by Lake Bykal in Russia.

Lake Michigan is the sixth largest lake in the world and is the only one of the Great Lakes that lies entirely within the boundaries of the United States. The lake has a relatively smooth, gently sloping bottom in its southern third, and an irregular bottom with extensive reef systems and a number of islands in the northern two thirds. Green Bay, in the northwest part of the lake, is 118 miles long and averages 23 miles in width.

Great Lakes Comparison
	Michigan	Superior	Huron	Erie	Ontario
Low Water Datum (ft)	576.8	600.0	576.8	568.6	242.8
Surface Area (sq mi)	22,309	31,793	22,923	9,841	7,326
Mean Depth (ft)	269	494	195	56	283
Maximum Depth (ft)	924	1,333	750	210	802
Volume (cu mi)	1,136	2,974	849	104	393
Drainage Basin (sq mi)	67,909	81,093	73,700	32,361	32,026
Retention Time (yr)	99.1	196.0	22.6	2.6	6.0

Illinois has jurisdiction over 976,640 acres (7%) of the lake and only 63 miles (4%) of the total shoreline but has 65% of the population of the four states’ counties bordering Lake Michigan. Unlike the other states, Illinois has no permanent streams discharging into Lake Michigan.

Approximately 21 million pounds of fish are harvested from Lake Michigan each year (avg. 1993-2003). Chinook salmon comprised the greatest portion of the harvest at 7.5 million pounds in 2002, followed by lake whitefish at 4 million pounds.