Lake Superior, Lake Huron, Lake Michigan, Lake Ontario, and Lake Erie make up the Great Lakes system. The Great Lakes contain the largest freshwater supply in the world, holding approximately 18% of the world's freshwater supply and 84% of North America's freshwater supply. They are located along the southern edge of the Canadian Shield and cover more than 94,000 square miles (245,000 square kilometers). Say no to plagiarism. Get a tailor-made essay on “Why Violent Video Games Should Not Be Banned”? Get the original essay. As five massive lakes, they provide the foundation for billions of dollars in manufacturing, shipping, commerce, fishing, forestry, agriculture, energy and tourism. The Great Lakes Basin is home to a diverse ecosystem and employment opportunities that are essential to the sustainability of the region. How were the Great Lakes formed? The five Great Lakes exist thanks to ice and glacial movements. More than a million years ago, huge glaciers covered the earth. Their weight depressed the ground where rivers existed before glaciers slid south from the North Pole. About 20,000 years ago, as Earth's climate warmed, the last continental ice sheet retreated northward. The glacier was up to 3 km thick and so powerful and heavy that it scraped the Earth's surface to create lake basins. Melt water from the retreating glacier filled the created pools. About 3,500 to 4,000 years ago, the Great Lakes reached their modern level and size. The Lake System: In addition to the five interconnected lakes, the Great Lakes system also includes Lake St. Clair. Lake St. Clair is a small lake located between Lake Erie and Lake Huron. These lakes are connected by the St. Marys River, the St. Clair River, the Detroit River and the Niagara River. The St. Marys River flows 60 miles from Lake Superior to Lake Huron. The St. Clair River and the Detroit River connect Lake Huron to Lake Erie. Together, these two rivers flow 89 miles between the two lakes. The Niagara River flows from Lake Erie to Lake Ontario. According to the 1985 International Great Lakes Datum, the average elevation of the Great Lakes ranges from 597 feet (182 meters) on Lake Superior to 242 feet (74 meters) on Lake Ontario. Keep in mind: this is just a sample. Get a custom paper now written by our expert writers.Get a custom essayWhy is it important? Why care? Recently, water levels in the Great Lakes have declined. This is due to greater evaporation caused by warmer than normal temperatures. Milder winters and below-average snowfall have also contributed to the lake's falling water levels. We must act on this issue as 40 billion citizens of Canada and the United States rely on the Great Lakes as a direct source of drinking water. Water is one of the most important substances on Earth, as plants, animals and humans depend on it to survive. So not only does it affect us, but also the ecosystem and biodiversity around us..