The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes spanning the Canada–United States border. The five lakes are Superior, Michigan, Huron, Erie, and Ontario (though hydrologically, Michigan and Huron are a single body of water, joined at the Straits of Mackinac). The Great Lakes Waterway enables modern travel and shipping by water among the lakes. The lakes connect ultimately to the Atlantic Ocean via the Saint Lawrence River as their primary drainage outflow. The lakes are also connected to the Mississippi River basin through the Illinois Waterway.
The Great Lakes are the largest group of freshwater lakes on Earth by total area and the second-largest by total volume. They contain more than 20% of the world's surface fresh water by volume. The total surface is , and the total volume (measured at the low water datum) is , slightly less than the volume of Lake Baikal (, 22–23% of the world's surface fresh water). Because of their sea-like characteristics, such as rolling waves, sustained winds, strong currents, great depths, and distant horizons, the five Great Lakes have long been called inland seas. Depending on how it is measured, by surface area, either Lake Superior or Lake Michigan–Huron is the second-largest lake in the world and the largest freshwater lake. Lake Michigan is the largest lake, by surface area, that is entirely within one country, the United States.
The Great Lakes began to form at the end of the Last Glacial Period around 14,000 years ago, as retreating ice sheets exposed the basins they had carved into the land, which then filled with meltwater. The lakes have been a major source for transportation, migration, trade, and fishing, serving as a habitat to many aquatic species in a region with much biodiversity. The surrounding region is called the Great Lakes region, which includes the Great Lakes megalopolis. Major cities within the region include, on the American side, from east to west, Rochester, Buffalo, Cleveland, Detroit, Chicago, Milwaukee, and Duluth; and, on the Canadian side, Toronto, Mississauga and Hamilton.
Geography
Though the five lakes lie in separate basins, they form a single, naturally interconnected body of fresh water, within the Great Lakes Basin. As a chain of lakes and rivers, they connect the east-central interior of North America to the Atlantic Ocean. From the interior to the outlet at the Saint Lawrence River, water flows from Superior to Huron and Michigan, southward to Erie, and finally northward to Lake Ontario. The lakes drain a large watershed via many rivers and contain approximately 35,000 islands. There are also several thousand smaller lakes, often called "inland lakes", within the basin.
The surface area of the five primary lakes combined is roughly equal to the size of the United Kingdom, while the surface area of the entire basin (the lakes and the land they drain) is about the size of the United Kingdom and France combined. Lake Michigan is the only one of the Great Lakes that is entirely within the United States; the others form a water boundary between the United States and Canada. The lakes are divided among the jurisdictions of the Canadian province of Ontario and the U.S. states of Michigan, Wisconsin, Minnesota, Illinois, Indiana, Ohio, Pennsylvania, and New York. Both the province of Ontario and the state of Michigan include in their boundaries portions of four of the lakes. The province of Ontario does not border Lake Michigan, and the state of Michigan does not border Lake Ontario. New York and Wisconsin's jurisdictions extend into two lakes, and each of the remaining states into one of the lakes.
Bathymetry + Relative elevations, average depths, maximum depths, and volumes of the Great Lakes Notes: The area of each rectangle is proportional to the volume of each lake. All measurements at Low Water Datum. Source: United States Environmental Protection Agency
Lake ErieLake HuronLake MichiganLake OntarioLake Superior Surface area Water volume Elevation Average depth Maximum depth Major settlementsSee List of cities on the Great Lakes for a complete list. Buffalo, NYErie, PACleveland, OHDetroit, MILorain, OHToledo, OHSandusky, OHWindsor, ON Alpena, MIBay City, MICollingwood, ONOwen Sound, ONPort Huron, MISarnia, ON Chicago, ILWaukegan, ILGary, INGreen Bay, WISheboygan, WIMilwaukee, WIKenosha, WIRacine, WIMuskegon, MITraverse City, MI Hamilton, ONKingston, ONMississauga, ONOshawa, ONRochester, NYSt. Catharines, ONToronto, ON Duluth, MNMarquette, MISault Ste. Marie, MISault Ste. Marie, ONSuperior, WIThunder Bay, ONAs the surfaces of Lakes Superior, Huron, Michigan, and Erie are all approximately the same elevation above sea level, while Lake Ontario is significantly lower, and because the Niagara Escarpment precludes all natural navigation, the four upper lakes are commonly called the "upper great lakes". This designation is not universal. Those living on the shore of Lake Superior often refer to all the other lakes as "the lower lakes", because they are farther south. Sailors of bulk freighters transferring cargoes from Lake Superior and northern Lake Michigan and Lake Huron to ports on Lake Erie or Ontario commonly refer to the latter as the lower lakes and Lakes Michigan, Huron, and Superior as the upper lakes. This corresponds to thinking of lakes Erie and Ontario as "down south" and the others as "up north". Vessels sailing north on Lake Michigan are considered "upbound" even though they are sailing toward its effluent current.
Primary connecting waterways
The St. Marys River, including the Soo Locks, connects Lake Superior to Lake Huron, via the North Channel. The Straits of Mackinac connect Lake Michigan to Lake Huron (the two are hydrologically one lake). The St. Clair River connects Lake Huron to Lake St. Clair. The Detroit River connects Lake St. Clair to Lake Erie. The Niagara River, including Niagara Falls, connects Lake Erie to Lake Ontario. The Welland Canal, bypassing the Niagara River, connects Lake Erie to Lake Ontario. The Saint Lawrence River and the Saint Lawrence Seaway connect Lake Ontario to the Gulf of Saint Lawrence, which connects to the Atlantic Ocean.
Secondary connecting waterways The Chicago River and Calumet River systems connect the Great Lakes Basin to the Mississippi River System through human-made alterations and canals.
Lake Michigan–Huron
Lakes Huron and Michigan are sometimes considered a single lake, called Lake Michigan–Huron, because they are one hydrological body of water connected by the Straits of Mackinac. The straits are wide and deep; the water levels rise and fall together and the flow between Michigan and Huron frequently reverses direction.
Large bays and related significant bodies of water Lake Nipigon, connected to Lake Superior by the Nipigon River, is surrounded by sill-like formations of mafic and ultramafic igneous rock hundreds of meters high. The lake lies in the Nipigon Embayment, a failed arm of the triple junction (centered beneath Lake Superior) in the Midcontinent Rift System event, estimated at 1.1 billion years ago. Thunder Bay (Ontario) is a large bay on the north shore of Lake Superior bordered to the east by the Sibley Peninsula in northern Ontario. Thunder Bay (Michigan) is a bay on the west side of Lake Huron in Michigan. Chequamegon Bay is an inlet of Lake Superior south of the Apostle Islands and the Bayfield Peninsula in northern Wisconsin. Keweenaw Bay is an arm of Lake Superior southeast of the Keweenaw Peninsula. Whitefish Bay is a large bay on the eastern end of Lake Superior which leads to the outflow of the lake into the St. Marys River. Lake Winnebago, connected to Green Bay by the Fox River, serves as part of the Fox–Wisconsin Waterway and is part of a larger system of lakes in Wisconsin known as the Winnebago Pool. Green Bay is an arm of Lake Michigan along the south coast of the Upper Peninsula of Michigan and the east coast of Wisconsin. It is separated from the rest of the lake by the Door Peninsula in Wisconsin, the Garden Peninsula in Michigan, and the chain of islands between them, all of which were formed by the Niagara Escarpment. The north end of Green Bay consists of Big Bay de Noc and Little Bay de Noc. Grand Traverse Bay is an arm of Lake Michigan on Michigan's west coast and is one of the largest natural harbors in the Great Lakes. The bay is divided into east and west arms by the Old Mission Peninsula. The bay has one major island, Power Island. Its name is derived from Jacques Marquette's crossing of the bay from Norwood to Northport which he called La Grande Traversee. Georgian Bay is an arm of Lake Huron, extending northeast from the lake entirely within Ontario. The bay, along with its narrow westerly extensions of the North Channel and Mississagi Strait, is separated from the rest of the lake by the Bruce Peninsula, Manitoulin Island, and Cockburn Island, all of which were formed by the Niagara Escarpment. Lake Nipissing, connected to Georgian Bay by the French River, contains two volcanic pipes, which are the Manitou Islands and Callander Bay. These pipes were formed by a violent, supersonic eruption of deep origin. The lake lies in the Ottawa-Bonnechere Graben, a Mesozoic rift valley that formed 175 million years ago. Lake Simcoe, connected to Georgian Bay by the Severn River, serves as part of the Trent–Severn Waterway, a canal route traversing Southern Ontario between Lakes Ontario and Huron. Saginaw Bay, an extension of Lake Huron into the Lower Peninsula of Michigan, fed by the Saginaw and other rivers, has the largest contiguous freshwater wetland in the United States. Lake St. Clair, connected with Lake Huron to its north by the St. Clair River and with Lake Erie to its south by the Detroit River. Although it is 17 times smaller in area than Lake Ontario and only rarely included in the listings of the Great Lakes, proposals for its official recognition as a Great Lake are occasionally made, which would affect its inclusion in scientific research projects designated as related to "The Great Lakes". Sandusky Bay is a bay on Lake Erie in northern Ohio. Long Point Bay is a bay on the north shore of Lake Erie in Ontario. Hamilton Harbour is a harbor on the western tip of Lake Ontario. The Bay of Quinte is a long and narrow bay on the north shore of Lake Ontario.
Islands
Dispersed throughout the Great Lakes are approximately 35,000 islands. The largest among them is Manitoulin Island in Lake Huron, the largest island in any inland body of water in the world. The second-largest island is Isle Royale in Lake Superior. Both of these islands are large enough to contain multiple lakes themselves—for instance, Manitoulin Island's Lake Manitou is the world's largest lake on a freshwater island. Some of these lakes even have their own islands, like Treasure Island in Lake Mindemoya in Manitoulin Island.
Peninsulas
The Great Lakes have several peninsulas between them, most prominently the Upper Peninsula, the Lower Peninsula, and the Ontario Peninsula. Population centers on these peninsulas include Grand Rapids, Flint, and Detroit in Michigan along with London, Hamilton, Brantford, and Toronto in Ontario. Other significant peninsulas in the Great Lakes include the Sibley, Bayfield, Keweenaw, Door, Garden, Leelanau, Thumb, Bruce, and Niagara peninsulas.
Shipping connection to the ocean