About Lake Michigan

Geography and Physical Characteristics

Lake Michigan is one of the five Great Lakes of North America and the only one located entirely within the United States. It covers portions of Illinois, Indiana, Michigan, and Wisconsin. Lake Michigan is connected directly to Lake Huron, into which it drains, through the broad Straits of Mackinac. This hydrologic connection through the Straits keeps the water levels of the two lakes in equilibrium, causing them to behave in many ways as though they are one lake. Water flows into Lake Michigan from several rivers in the 45,600 square mile Lake Michigan drainage basin, including the Fox-Wolf, the Grand, the St. Joseph, and the Kalamazoo rivers, among others. In addition to the main flow, some of the waters of Lake Michigan have been diverted into the Mississippi River basin via the Chicago River.

Facts About Lake Michigan

• Lake Michigan is 307 miles long and 118 miles across at its widest point.
• Water levels on Lake Michigan have varied by a bit more than six feet during the roughly 100-year period of record. Water levels exhibit an annual cycle, with the highest levels typically occurring in late summer and the lowest in the winter.
• It has an average depth of 279 feet (85 meters) but that varies considerably from place to place. The maximum depth of 923 feet (281 meters) is found in the Chippewa Basin, which dominates much of the northern half of the lake.
• It contains approximately 1,180 cubic miles of water, making it:
  • The largest freshwater lake in the United States
  • The second largest Great Lake (by volume)
  • The fifth largest lake in the world
• It has a hydrologic residence time [PDF] of 62 years, which means water flushes through it much more slowly than all the other Great Lakes – with the exception of Lake Superior.
• Lake Michigan has some 1,638 miles of shoreline, of which 45 miles lie in Indiana. People from all over the world enjoy its many beaches.
• Lake Michigan’s ecosystem contains the world’s largest collection of freshwater sand dunes, which formed [PDF] along the eastern shorelines due to the combined action of wind and waves against glacial moraines long ago.

Ecology and Wildlife

The Nature Conservancy and Michigan Natural Features Inventory published a technical report in 2012 about Michigami: Great Water – Strategies to Conserve the Biodiversity of Lake Michigan [PDF]. These excerpts about Lake Michigan and its associated biodiversity are from pages 3 and 17 of the report:

“Lake Michigan … is an ecologically rich and globally significant ecosystem. ...its coastline harbors boreal forests and coastal fens in the north and dry sand prairies and oak savannas in the south. In fact, Indiana Dunes National Lakeshore is among the most biologically rich of all U.S. national parks, on a per‐area basis, due to the co‐occurrence of southern and northern species. ...the shorelines provide food and shelter for millions of migrating birds every year. In the water, the variety of nearshore habitats provide spawning or nursery grounds for many fish species, supporting important fisheries; migratory fish connect the lake to its tributaries...”

“These natural communities provide habitat to a large number of rare species, many of which are only found in the Great Lakes region. Examples of globally significant plants found in the Lake Michigan coastal zone include: Pitcher’s thistle..., Houghton’s goldenrod..., Dwarf lake iris...,  prairie white‐fringed orchid  ..., ram’s head lady’s slipper..., spatulate moonwort..., ginseng..., prairie moonwort..., and lakeside daisy... Examples of globally significant animals found in the Lake Michigan coastal zone include: Piping plover..., Hine’s Emerald dragonfly..., and Lake Huron locust...”

Why Biodiversity Matters

Biodiversity is an indication of the health of an ecosystem. Problems with biodiversity indicate stress on an ecosystem, which can be caused by:

• resource overuse (including over-hunting, over-logging, or over-fishing)
• habitat destruction or division
• introduction of invasive species
• pollution

When an ecosystem’s biodiversity begins to decrease, it can take years to recover. This is because organisms need to move back from other areas. Plus, if the number of total individuals in a species drops too low, the species becomes less genetically diverse (inbred) and is less able to fight off threats. In that case, it will often go extinct. Once a species disappears, there is no way to bring it back. Breeding programs can help, but many species do not respond very well to such efforts; it is far better to prevent a species from becoming endangered in the first place.

Many species provide, or have the potential to provide, value to human beings. The Dwarf lake iris, Houghton’s goldenrod, and Hine’s Emerald dragonfly are examples of species which add to the aesthetic quality of the outdoors that draws millions of visitors to Indiana’s Lake Michigan beaches each year. In addition, people are constantly finding new uses for plants and animals, including as sources of food and medicine. A 2001 study stated that, of the 252 drugs considered as basic and essential by the World Health Organization (WHO), 11% were exclusively of plant origin (S.M. Rates, 2001 [PDF]). However, even those organisms that provide no obvious benefit to people still have a place in the ecosystem’s food web.

People and Industry

Lake Michigan’s shoreline provides a home to over 10 million annual residents and includes the nation’s third largest city – Chicago, Illinois.

Many agricultural and industrial products such as iron ore, coal, limestone, metals, petroleum, coke, and chemicals are derived from the Lake Michigan basin's resources. The water of Lake Michigan serves many purposes. It supports large commercial and sport fishing industries. It provides industrial process and cooling water, and water for agricultural irrigation. Fleets of freighters pass over the lake carrying bulk commerce items. Lake Michigan serves as a source of drinking water, as a place for swimming and fishing, as a scenic wonderland, and as a drainage basin for municipal and industrial waste and runoff from the surrounding lands.

Beaches and Recreation

Lake Michigan provides extensive recreational opportunities, fueling a thriving tourism industry in the Great Lakes states. Lake Michigan visitors can enjoy a wide array of activities, including swimming at one of its beautiful beaches, sport fishing and recreational boating out of one of its many marinas, and hiking and camping at one of the many state and national parks located along the shoreline. There truly is something for everyone!