What is the significance of the Great Lakes?

The Great Lakes are five interconnected freshwater lakes shared between Canada and the United States, holding about 21 per cent of the world's surface fresh water. From west to east they are Lake Superior, Lake Michigan (entirely in the United States), Lake Huron, Lake Erie, and Lake Ontario. The four shared lakes border the Canadian province of Ontario, and the international boundary runs through them under the 1908 International Boundary Treaty.

Lake Superior is the largest freshwater lake in the world by surface area at 82,100 square kilometres and the deepest of the Great Lakes at 406 metres. Lake Erie is the shallowest at 64 metres and the most ecologically stressed by agricultural runoff. The system drains through the Niagara River and the St. Lawrence River to the Atlantic Ocean, with shipping reaching the Great Lakes via the St. Lawrence Seaway opened on April 25, 1959. The Welland Canal between Lake Erie and Lake Ontario lifts ships 99.5 metres around Niagara Falls.

The Great Lakes basin is home to roughly 35 million people, including about nine million Canadians in the Toronto-Hamilton-Niagara, Sarnia, Windsor, and Thunder Bay regions. The lakes provide drinking water for these communities and support fisheries, recreation, and major industrial regions including the Hamilton steel mills and the Sarnia chemical industry. The International Joint Commission, established by the Boundary Waters Treaty of 1909, manages cross-border water issues.

Indigenous nations including the Anishinaabe (Ojibwe, Odawa, and Potawatomi) and the Haudenosaunee Confederacy have lived in the Great Lakes basin for thousands of years and continue to assert treaty rights. Important sites include the Sault Ste. Marie locks (1855), the Welland Canal (current canal opened 1932), and the protected ecosystems of Bruce Peninsula National Park, Pukaskwa National Park, and the Thirty Thousand Islands of Georgian Bay.