Welcome to the 31,000 Islands of the Great Lakes

Laurentia at a Glance:

  • Surface area: 244,079 square kms.

  • Watershed’s surface: 521,830 square kms.

  • Water Retention time: 2.7-191 years

  • Approximately 40,000,000 inhabitants

Information by Ivette Bolender of Biohabitats and the Great Lakes Guide

Less than 20,000 years ago, as the earth’s climate warmed and the last glacial continental ice sheet retreated, a system of interconnecting bodies of water began to form – a system we now know as the Laurentian Great Lakes. The Great Lakes, comprised of five large lakes, one small lake, four connecting channels and a seaway, span over 95,000 square miles (245,759 square km), and are now one of the world’s most important natural resources.

The Laurentia Bioregion is a land of waters. The unparalleled, natural beauty of the Great Lakes inspires a sense of wonder and possibility. They are one of the world’s most significant water resources and the most extensive freshwater system on Earth. The Great Lakes — Superior, Michigan, Huron, Erie, and Ontario — represent thousands of years of history and continue to play an important role in the physical and cultural heritage of North America. They are critical to the social and economic vitality of the entire North American continent.

The Great Lakes watershed, or Great Lakes basin, is defined by watersheds that drain into the Great Lakes. A watershed is an area of land where all of the water that falls on it drains into the same outlet — for example, a stream, river, or lake. For this reason, a watershed is also called a drainage basin or catchment. A watershed is made up of surface water (from lakes, streams, wetlands, and reservoirs) and all underlying groundwater. As water continues to move downward, streams and rivers may join with larger lakes and, eventually, the ocean.

Great Lakes Guide combines the watersheds of the five Great Lakes, the Ottawa River, and the St. Lawrence River to bring you the full Great Lakes basin. The entire basin covers about 240,000 km² (94,000 square miles). The diagram below shows the movement of water as it flows through the connecting channels of the Great Lakes, through the St. Lawrence seaway to the Atlantic Ocean.

The Great Lakes are a chain of five large, interconnected bodies of water. These five lakes, together with the St. Lawrence River, contain 20% of the world’s fresh water and form the largest surface freshwater system in the world. There are 31,407 Great Lakes islands. They range in size from a small boulder to over 100,000 acres. In comparison, the Caribbean Islands consist of only about 7,000 islands.

The Great Lakes basin is home to approx. 40 million people, nestled among 2 countries, 2 provinces, 8 states, and 64 First Nations.



So what is so special about these Great Lakes Islands? Great Lakes Islands are the largest fresh water and inland system in the world, with biodiversity that is of global significance. The largest fresh water island is Manitoulin (80 miles long) in Lake Huron. The majority of the islands (about 22,000) are in the Georgian Bay of Lake Huron. Many of the larger islands are in Lake Superior. A little over 3,000 are in the U.S., with the remainder in Canadian waters. The islands make up one percent of the land area of the Great Lakes, yet they provide 10 percent of the endangered, threatened and rare species habitats that live in the basin.

The Great Lakes region is unique: It has one of the richest and most ecologically diverse ecosystems on the planet. It encompasses forest, wetland, and grassland habitats, and is home to over 4,000 species of plants, fish, and wildlife. This ecosystem boasts some of the most impressive and diverse habitats in the world — from rocky peninsulas and towering cliffs, to vast marshlands and immense sand dunes.

The islands provide habitat for fish and colonial nesting waterbirds, stopover sites for migratory birds, and a refuge for endangered and threatened species. They can provide relatively undisturbed habitat that may have fewer predators, allowing vulnerable species to survive.

The Great Lakes Islands face numerous threats. Many have recreation, commercial and residential use.  Their popularity has ironically been the prime cause of the unintentional destruction of natural plant and animal communities. Native plant and animal communities on and around islands are vulnerable to invasion by non-native species (purple loosestrife, zebra and quagga mussels). Other threats include sewage disposal, toxic contamination through heavy metals and pesticides, runoff from agricultural, urbanization and air pollution. Stresses also include habitat loss, fragmentation and climate change.

Of all of the islands in the Great Lakes, Isle Royale catches my interest because of its one sentence description: There’s no place like it, for Isle Royale IS what America WAS. Here is some history.

The French, lured by the fur trade, named the island in 1671. Isle Royale became U.S. territory in 1783 and was ceded to the United States by the Chippewa in 1843. It was mined for copper from 1843 to 1899. Large areas of forest were burned to expose the ore and to build settlements. In the early 1900s the island became a popular vacation retreat.

Isle Royale National Park was established in 1933 and is the U.S.’s only island national park. It spans 571,790 acres (231,575 hectares) and consists of about 200 islands, in Lake Superior, NW Michigan. Isle Royale, 210 sq mi (544 sq km), is the largest island in Lake Superior. A prime example of Northwoods Wilderness, Isle Royale was designated an International Biosphere Reserve (IBR) by the United Nations, giving it international scientific and education significance. (There are only 496 IBR in the world.) Glaciated, the island has many lakes, streams, and inlets and remains a roadless, forested wilderness. Its abundant wildlife includes beaver, fox, moose, timber wolves, and many birds.

In spite of their large size, the Great Lakes are extremely vulnerable.

Each year, only about 1% of the water in the lakes leaves the basin via the St. Lawrence River. Because water exits the system so slowly, the Great Lakes are essentially a closed system. Until European settlement, the Great Lakes ecosystem was also considered “ecologically naïve,” meaning that historically, its vulnerable animal and plant species were isolated. Now, they are left uniquely exposed to stressors such as pollution, invasive species, and habitat degradation.

Past and present neglect of the system — unsustainable use, discharging of harmful chemicals, and climate change — have led to serious consequences for native species and the health of the Great Lakes. The four biggest, ongoing issues facing the Great Lakes are habitat destruction, sewage pollution, river damming and diversion, and land-use runoff.

The Great Lakes have provided us with invaluable resources — drinking water