Great Lakes

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 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. Because of their sea-like characteristics, such as rolling waves and strong currents, the five Great Lakes have long been called inland seas.

The Great Lakes began to form at the end of the Last Glacial Period around 14,000 years ago. They have been important for transportation, trade, and fishing, and they provide a home to many aquatic species. Major cities around the lakes include Buffalo, Cleveland, Detroit, Chicago, Milwaukee, Duluth, Toronto, Mississauga and Hamilton.

Geography

The five Great Lakes—Superior, Michigan, Huron, Erie, and Ontario—are large, connected freshwater lakes along the border between the United States and Canada. Though they sit in separate basins, they work together as one big water system. Water flows from Lake Superior to Lake Huron and Lake Michigan, then southward to Lake Erie, and finally northward to Lake Ontario. These lakes drain a large area through many rivers and hold around 35,000 islands. There are also thousands of smaller lakes nearby.

The combined surface area of the five main lakes is about the size of the United Kingdom. Lake Michigan is the only one completely inside the United States; the others form a border between the United States and Canada. The lakes lie in different areas, including the Canadian province of Ontario and several U.S. states such as Michigan, Wisconsin, Minnesota, Illinois, Indiana, Ohio, Pennsylvania, and New York.

A map of the Great Lakes Basin showing the five sub-basins. Left to right they are: Superior (magenta); Michigan (cyan); Huron (green); Erie (yellow); Ontario (red).

Lakes Superior, Huron, Michigan, and Erie sit roughly at the same height above sea level, while Lake Ontario is much lower. Because of this height difference and natural barriers, the four upper lakes are often called the "upper great lakes." People sometimes call Lakes Erie and Ontario the "lower lakes" because they are farther south.

Primary connecting waterways

The St. Marys River, including the Soo Locks, links Lake Superior to Lake Huron through the North Channel.
The Straits of Mackinac connect Lake Michigan to Lake Huron (these two are actually one lake).
The St. Clair River links Lake Huron to Lake St. Clair.
The Detroit River links Lake St. Clair to Lake Erie.
The Niagara River, including Niagara Falls, links Lake Erie to Lake Ontario.
The Welland Canal, going around Niagara River, links Lake Erie to Lake Ontario.
The Saint Lawrence River and the Saint Lawrence Seaway link Lake Ontario to the Gulf of Saint Lawrence, which leads to the Atlantic Ocean.

Secondary connecting waterways

The Chicago River and Calumet River systems link the Great Lakes to the Mississippi River System through human-made canals.

Great Lakes/St. Lawrence River watershed

Lake Michigan–Huron

Main article: Lake Michigan–Huron

Lakes Huron and Michigan are often thought of as one lake, called Lake Michigan–Huron, because they are connected by the Straits of Mackinac. The straits are five miles wide and 120 feet deep; the water levels of both lakes rise and fall together, and the flow between them can change direction.

Large bays and related significant bodies of water

Lake Nipigon, linked to Lake Superior by the Nipigon River, is surrounded by high rock walls. It lies in a special area formed about 1.1 billion years ago.
Thunder Bay is a big bay on the north shore of Lake Superior.
Chequamegon Bay is an inlet of Lake Superior south of the Apostle Islands.
Keweenaw Bay is part of Lake Superior southeast of the Keweenaw Peninsula.
Whitefish Bay is a large bay on Lake Superior’s eastern end.
Lake Winnebago, linked to Green Bay by the Fox River, is part of a bigger lake system in Wisconsin.
Green Bay is an arm of Lake Michigan along Michigan’s Upper Peninsula and Wisconsin’s coast.
Grand Traverse Bay is a big harbor on Lake Michigan’s west coast.
Georgian Bay is an arm of Lake Huron in Ontario.
Lake Nipissing, linked to Georgian Bay by the French River, contains two special islands formed by old volcanic activity.
Lake Simcoe, linked to Georgian Bay by the Severn River, is part of a canal system in Southern Ontario.
Thunder Bay is a bay on Lake Huron’s west side in Michigan.
Saginaw Bay is an extension of Lake Huron in Michigan, home to large wetlands.
Lake St. Clair, linked to Lake Huron and Lake Erie by rivers, is sometimes suggested to be an official Great Lake.
Sandusky Bay is a bay on Lake Erie in Ohio.
Long Point Bay is a bay on Lake Erie’s north shore in Ontario.
Hamilton Harbour is a harbor at the west tip of Lake Ontario.
The Bay of Quinte is a long, narrow bay on Lake Ontario’s north shore.

Islands

The Great Lakes hold around 35,000 islands. The biggest is Manitoulin Island in Lake Huron—the largest island in any inland water in the world. The second largest is Isle Royale in Lake Superior. These islands are so big they contain lakes of their own, like Lake Manitou on Manitoulin Island.

Peninsulas

The Great Lakes have several peninsulas between them, such as the Upper Peninsula, the Lower Peninsula, and the Ontario Peninsula. Big cities like Grand Rapids, Flint, Detroit, London, Hamilton, Brantford, and Toronto sit on these peninsulas. Other important peninsulas include the Sibley, Bayfield, Keweenaw, Door, Garden, Leelanau, Thumb, Bruce, and Niagara peninsulas.

Shipping connection to the ocean

Even though the Saint Lawrence Seaway and Great Lakes Waterway let ocean ships reach the Great Lakes, larger modern ships can’t fit through the locks. Most trade is in bulk materials, and big cargo ships can travel the whole system and reach the Atlantic. Smaller ships stay within the lakes. Some barges can reach the Gulf of Mexico through the Illinois Waterway.

The Great Lakes connect to the Gulf of Mexico through the Chicago Sanitary and Ship Canal and rivers. Pleasure boats can enter the Great Lakes through the Erie Canal and Hudson River in New York.

Water levels

The lakes get water from rain, rivers, and underground springs. Human activities, like moving water to other places or using it for power plants, can change the lake levels. The levels of the lakes have gone up and down over time. For example, in 2013, Lakes Superior, Erie, and Michigan-Huron were at record low levels, but in 2020, they reached record highs. Lake Ontario’s level has stayed fairly steady.

Small changes in water level caused by the sun and moon happen, but they are tiny compared to other forces. The main things that change lake levels are weather and climate. The flow from Lakes Superior and Ontario is controlled, but the flow from Michigan-Huron and Erie is not.

Ice cover

How much ice covers the Great Lakes each year changes a lot depending on the winter weather. Ice usually starts forming in December and peaks in February or March. Some winters, like 2013–2014, almost all of the lakes froze (over 92%), but in milder winters like 2023–2024, less than 20% was covered. Over the past few decades, there has been less ice overall, matching warmer temperatures in the area.

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 Erie	Lake Huron	Lake Michigan	Lake Ontario	Lake Superior
Surface area	9,910 square miles (25,667 km²)	23,000 square miles (59,570 km²)	22,300 square miles (57,757 km²)	7,340 square miles (19,011 km²)	31,700 square miles (82,103 km²)
Water volume	480 km³ (116 cu mi)	3,500 km³ (850 cu mi)	4,900 km³ (1,180 cu mi)	1,640 km³ (393 cu mi)	12,000 km³ (2,900 cu mi)
Elevation	174 m (571 ft)	176 m (577 ft)	176 m (577 ft)	75 m (246 ft)	182.9 m (600.0 ft)
Average depth	19 m (62 ft)	59 m (195 ft)	85 m (279 ft)	86 m (283 ft)	147 m (483 ft)
Maximum depth	64 m (210 ft)	228 m (748 ft)	282 m (925 ft)	245 m (804 ft)	406 m (1,333 ft)
Major settlements	Buffalo, NY Erie, PA Cleveland, OH Detroit, MI Lorain, OH Toledo, OH Sandusky, OH Windsor, ON	Alpena, MI Bay City, MI Collingwood, ON Owen Sound, ON Port Huron, MI Sarnia, ON	Chicago, IL Waukegan, IL Gary, IN Green Bay, WI Sheboygan, WI Milwaukee, WI Kenosha, WI Racine, WI Muskegon, MI Traverse City, MI	Hamilton, ON Kingston, ON Mississauga, ON Oshawa, ON Rochester, NY St. Catharines, ON Toronto, ON	Duluth, MN Marquette, MI Sault Ste. Marie, MI Sault Ste. Marie, ON Superior, WI Thunder Bay, ON

Etymology

Lake Erie

1675 French map, published shortly before the voyage of Le Griffon. Lake Michigan is named Lake Illinois (the name change is first recorded in 1681), and Lake Ontario is named Lake Frontenac, after the then-governor of New France.

The name comes from the Erie tribe, a shorter form of the Iroquoian word erielhonan, meaning "long tail".

Lake Huron

It was named after the Wyandot people, also called "Hurons", by the first French explorers. The Wyandot called the lake karegnondi, which means "Freshwater Sea", "Lake of the Hurons", or simply "lake".

Lake Michigan

Lakes Superior, Michigan, Huron, and Erie, photographed from the Sentinel-3B satellite in June 2022, Lake Ontario is not visible in this image.

The name comes from the Ojibwe word mishi-gami, meaning "great water" or "large lake".

Lake Ontario

It comes from the Wyandot word ontarí'io, meaning "lake of shining waters".

Lake Superior

This name is an English translation of the French term lac supérieur, meaning "upper lake", because it sits higher and drains into Lake Huron. The Ojibwe call it gichi-gami, meaning "big water" or "large lake". It became popular in songs and poems, like in Gordon Lightfoot's 1976 song "The Wreck of the Edmund Fitzgerald" and Henry Wadsworth Longfellow's 1855 poem, The Song of Hiawatha.

Statistics

The Great Lakes hold a lot of fresh water—about 21% of all the fresh water on Earth's surface. There are enough gallons to cover the lower 48 U.S. states in about 9.5 feet of water!

These lakes cover an area of roughly 94,250 square miles, which is nearly as big as the entire United Kingdom. If you traveled along their shorelines, it would be about the same distance as going halfway around the world! In winter, something cool happens: ice volcanoes can form when storms push water through the ice, creating icy mounds. This only happens clearly in the Great Lakes and helps protect some shores from wear and tear.

Geology

A diagram of the formation of the Great Lakes

The Great Lakes were formed long ago, about 1.1 to 1.2 billion years back, when two large pieces of Earth's surface moved apart and created a deep valley. This valley later became Lake Superior. Later, around 570 million years ago, another crack formed, which helped create Lakes Ontario and Erie.

Near the end of the last big cold time, called the Last Glacial Period, huge glaciers moved away, leaving behind pools of water in the valleys they carved. These pools of water became the Great Lakes we know today. As the glaciers melted, they left behind islands and changed the shape of the land.

Climate

The location of common lake effect bands on the Great Lakes

The Great Lakes have a humid continental climate, with different temperature patterns in southern and northern areas. The lakes can change the weather around them. They often cause extra snow, called lake-effect snow, which can fall in narrow bands. This snow especially affects areas along the eastern shores of the lakes.

The lakes also help control temperatures, keeping summers cooler and protecting plants from early frost. This allows fruits and even grapes to grow in places that are usually too cold. The lakes can also make storms stronger, sometimes leading to severe weather and damage.

Ecology

The Great Lakes are a group of large, connected freshwater lakes along the border between Canada and the United States. They are Lake Superior, Lake Michigan, Lake Huron, Lake Erie, and Lake Ontario. Together, they hold about one-fifth of the world’s fresh surface water.

Generalized schematic of Great Lakes waterline ecosystem

Historically, the shores of these lakes were surrounded by forests, except near Lake Michigan where grasslands sometimes appeared. Human activities like logging, building cities, and farming have changed this. Today, Lake Superior’s shores are still mostly forested, while Lake Erie has the least forest cover due to more development. Some forests have grown back after being cut down.

The Great Lakes support many kinds of fish and other water animals. They are important for fishing, both for fun and for business. Over time, the number of fish has changed because of overfishing, dams blocking fish paths, and the arrival of new species that are not native to the lakes.

History

People have lived around the Great Lakes for thousands of years. After the big glaciers melted, Native American groups lived in the area around 10,000 BC. They traded with each other starting around 1000 AD, using copper from the region to make tools and decorations.

In 1818, after the War of 1812, two countries agreed to stop having battleships on the Great Lakes, though they still kept some coast guard boats. The first known ship to sail on the Great Lakes was Le Griffon, built by René-Robert Cavelier, Sieur de La Salle. It sailed in 1679. Later, canals were built, allowing boats to travel between the Great Lakes and the Atlantic Ocean and the Mississippi River. This helped people and goods move around more easily.

In the 1800s, many immigrants traveled by boat to the Great Lakes area, and cities grew up around the lakes. After railroads and roads were built, fewer people used boats for travel, but some boat services are still running today.

Today, most goods are moved by trains and trucks, but some ships still carry big loads like iron ore, coal, and limestone for making steel. Grain is also a big cargo on the lakes. Ships on the Great Lakes have special names and designs. Some are called “lakers,” and foreign ships are called “salties.”

During World War II, the United States Navy used two training ships on the Great Lakes. In 1998, Lake Champlain was briefly called the sixth Great Lake, but this was later changed back.

The fishing industry began on the Great Lakes around the time of the War of 1812. Fish was sent to markets, and the industry grew, especially around the fur trade. In the mid-1800s, fancy steamships carried passengers and goods around the lakes. Today, several ferry services operate on the Great Lakes, carrying passengers to islands.

Shipwrecks

The Great Lakes can be dangerous for ships because of big storms and hidden rocks. Many ships have sunk there, especially near Thunder Bay and Whitefish Point. One famous shipwreck is the SS Edmund Fitzgerald, which sank in 1975. The area around Whitefish Point is known as the “Graveyard of the Great Lakes” because so many ships have sunk there.

In 2007, the wreckage of the Cyprus was found. It sank in 1907 during a storm on Lake Superior. In 2008, divers found the wreck of the HMS Ontario in Lake Ontario. The last two warships to sink in the Great Lakes, the French minesweepers Inkerman and Cerisoles, are still missing. They vanished in Lake Superior in 1918 during a big snowstorm.

The Wisconsin Shipwreck Coast National Marine Sanctuary was created in 2021 to protect many important shipwrecks in Lake Michigan.

Economy

Shipping

Except when the water is frozen during winter, more than 100 ships work all year on the Great Lakes. These ships help move big amounts of goods like iron ore, grain, and potash. The Great Lakes Waterway connects all the lakes, and the Saint Lawrence Seaway links them to the Atlantic Ocean. Some ships are too big to use the Seaway and stay only on the Waterway and lakes. Big ports like Duluth-Superior, Chicago, Detroit, Cleveland, Twin Harbors, Hamilton and Thunder Bay are important for this shipping.

Recreation

Tourism and fun activities are very important for the Great Lakes. Small cruise ships, including some sailing ships, travel on the lakes. Fishing for salmon, whitefish, smelt, lake trout, bass, and walleye is a big business. Many people also enjoy water sports like yachting, sea kayaking, diving, kitesurfing, powerboating, and lake surfing. The Great Lakes Circle Tour is a special scenic road system that connects all of the Great Lakes and the Saint Lawrence River.

Legislation

In 1872, a treaty allowed the United States access to the St. Lawrence River and Lake Michigan, and gave similar access to the Dominion of Canada. In 1909, the International Joint Commission was created to help settle disagreements about water use and quality between the two countries, and to give advice on water issues.

There have been worries about taking water away from the Great Lakes. Some water is moved through the Chicago River to help ships travel, but treaties limit how much can be moved. Plans to sell water from the lakes to other places have caused concern.

In 1998, a Canadian company wanted to take water from Lake Superior to send to Asia, but after many people objected, the plan was stopped. After that, leaders from the Great Lakes states and the provinces of Ontario and Quebec worked on agreements to protect the lakes from most future water-taking plans. These agreements were signed in 2005.

The Great Lakes Restoration Initiative gets money from the U.S. government to help clean up harmful substances, restore wetlands and shorelines, and manage invasive species. The program was renewed to continue through 2026.