Lake Erie in the context of "Interstate 75"

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 21% of the world's surface fresh water by volume. The total surface is 94,250 square miles (244,106 km), and the total volume (measured at the low water datum) is 5,439 cubic miles (22,671 km), slightly less than the volume of Lake Baikal (5,666 cu mi or 23,615 km, 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.

Ontario is the southernmost province of Canada. Located in Central Canada, Ontario is the country's most populous province. As of the 2021 Canadian census, it is home to 38.5% of the country's population, and is the second-largest province by total area (after Quebec). Ontario is Canada's fourth-largest jurisdiction in total area of all the Canadian provinces and territories. It is home to the nation's capital, Ottawa, and its most populous city, Toronto, which is Ontario's provincial capital.

Ontario is bordered by the province of Manitoba to the west, Hudson Bay and James Bay to the north, and Quebec to the east and northeast. To the south, it is bordered by the U.S. states of (from west to east) Minnesota, Michigan, Ohio, Pennsylvania (through Lake Erie), and New York. Almost all of Ontario's 2,700 km (1,700 mi) border with the United States follows rivers and lakes: from the westerly Lake of the Woods, eastward along the major rivers and lakes of the Great Lakes/Saint Lawrence River drainage system. There is only about 1 km (5⁄8 mi) of actual land border, made up of portages including Height of Land Portage on the Minnesota border.

New York, also called New York State, is a state in the northeastern United States. Bordered by the New England states to the east, Canada to the north, and Pennsylvania and New Jersey to the south, its territory extends into both the Atlantic Ocean and the Great Lakes. New York is the fourth-most populous state in the United States, with nearly 20 million residents, and the 27th-largest state by area, with a total area of 54,556 square miles (141,300 km).

New York has a varied geography. The southeastern part of the state, known as Downstate, encompasses New York City, the most populous city in the United States; Long Island, with approximately 40% of the state's population, the nation's most populous island; and the cities, suburbs, and wealthy enclaves of the lower Hudson Valley. These areas are the center of the expansive New York metropolitan area and account for approximately two-thirds of the state's population. The larger Upstate area spreads from the Great Lakes to Lake Champlain and includes the Adirondack Mountains and the Catskill Mountains (part of the wider Appalachian Mountains). The east–west Mohawk River Valley bisects the more mountainous regions of Upstate and flows into the north–south Hudson River valley near the state capital of Albany. Western New York, home to the cities of Buffalo and Rochester, is part of the Great Lakes region and borders Lake Ontario and Lake Erie. Central New York is anchored by the city of Syracuse; between the central and western parts of the state, New York is prominently featured by the Finger Lakes, a popular tourist destination. To the south, along the state border with Pennsylvania, the Southern Tier sits atop the Allegheny Plateau, representing some of the northernmost reaches of Appalachia.

An algal bloom or algae bloom is a rapid increase or accumulation in the population of algae in fresh water or marine water systems. It may be a benign or harmful algal bloom.

Algal bloom is often recognized by the discoloration in the water from the algae's pigments. The term algae encompasses many types of aquatic photosynthetic organisms, both macroscopic multicellular organisms like seaweed and microscopic unicellular organisms like cyanobacteria. Algal bloom commonly refers to the rapid growth of microscopic unicellular algae, not macroscopic algae. An example of a macroscopic algal bloom is a kelp forest.

Dead zones are hypoxic (low-oxygen) areas in the world's oceans and large lakes. Hypoxia occurs when dissolved oxygen (DO) concentration falls to or below 2 mg of O₂/liter. When a body of water experiences hypoxic conditions, aquatic flora and fauna begin to change behavior in order to reach sections of water with higher oxygen levels. Once DO declines below 0.5 mg O₂/liter in a body of water, mass mortality occurs. With such a low concentration of DO, these bodies of water fail to support the aquatic life living there. Historically, many of these sites were naturally occurring. However, in the 1970s, oceanographers began noting increased instances and expanses of dead zones. These occur near inhabited coastlines, where aquatic life is most concentrated.

Coastal regions, such as the Baltic Sea, the northern Gulf of Mexico, and the Chesapeake Bay, as well as large enclosed water bodies like Lake Erie, have been affected by deoxygenation due to eutrophication. Excess nutrients are put into these systems by rivers, ultimately from urban and agricultural runoff and exacerbated by deforestation. These nutrients lead to high productivity that produces organic material that sinks to the bottom and is respired. The respiration of that organic material uses up the oxygen and causes hypoxia or anoxia.

The Wisconsin glaciation, also called the Wisconsin glacial episode, was the most recent glacial period of the North American ice sheet complex, peaking more than 20,000 years ago. This advance included the Cordilleran Ice Sheet, which nucleated in the northern North American Cordillera; the Innuitian ice sheet, which extended across the Canadian Arctic Archipelago; the Greenland ice sheet; and the massive Laurentide Ice Sheet, which covered the high latitudes of central and eastern North America. This advance was synchronous with global glaciation during the last glacial period, including the North American alpine glacier advance, known as the Pinedale glaciation. The Wisconsin glaciation extended from about 75,000 to 11,000 years ago, between the Sangamonian Stage and the current interglacial, the Holocene. The maximum ice extent occurred about 25,000–21,000 years ago during the last glacial maximum, also known as the Late Wisconsin in North America.

This glaciation radically altered the geography north of the Ohio River, creating the Great Lakes. At the height of the Wisconsin Episode glaciation, the ice sheet covered most of Canada, the Upper Midwest, and New England, as well as parts of Idaho, Montana, and Washington. On Kelleys Island in Lake Erie, northern New Jersey and in New York City's Central Park, the grooves left in rock by these glaciers can be easily observed. In southwestern Saskatchewan and southeastern Alberta a suture zone between the Laurentide and Cordilleran ice sheets formed the Cypress Hills, North America's northernmost point that remained south of the continental ice sheets. During much of the glaciation, sea level was low enough to permit land animals, including humans, to occupy Beringia (the Bering Land Bridge) and move between North America and Siberia. As the glaciers retreated, glacial lakes were breached in great glacial lake outburst floods such as the Kankakee Torrent, which reshaped the landscape south of modern Chicago as far as the Ohio and Mississippi Rivers.

The Cuyahoga River (see § Pronunciation) is a river located in Northeast Ohio that bisects the City of Cleveland and feeds into Lake Erie.

As Cleveland emerged as a major manufacturing center, the river became heavily affected by industrial pollution, so much so that it caught fire at least 14 times. When it did so on June 22, 1969, news coverage of the event helped to spur the American environmental movement. For many Americans, the Cuyahoga's burning helped connect urban decay with the environmental crisis at the time in many American cities. Since then, the river has been extensively cleaned up through the efforts of Cleveland's city government and the Ohio Environmental Protection Agency (OEPA). In 2019, the American Rivers conservation association named the Cuyahoga "River of the Year" in honor of "50 years of environmental resurgence".

Lake Ontario (French: Lac Ontario) is one of the five Great Lakes of North America. It is bounded on the north, west, and southwest by the Canadian province of Ontario, and on the south and east by the U.S. state of New York. The Canada–United States border spans the centre of the lake. On the Canadian side, the major cities are Kingston, Mississauga, Toronto, Hamilton, and St. Catharines. On the American side, the major cities are Rochester and Watertown.

The last in the Great Lakes chain, Lake Ontario serves as the outlet to the Atlantic Ocean via the Saint Lawrence River, comprising the western end of the Saint Lawrence Seaway. Its primary inlet is the Niagara River from Lake Erie. The Long Sault control dam, primarily along with the Moses-Saunders Power Dam regulates the water level of the lake.

Lake Huron (/ˈhjʊərɒn, -ən/ HURE-on, -⁠ən) is one of the five Great Lakes of North America. It is shared on the north and east by the Canadian province of Ontario and on the south and west by the U.S. state of Michigan. The name of the lake is derived from early French explorers who named it for the indigenous people they knew as Huron (Wyandot) inhabiting the region.Hydrologically, Lake Huron comprises the eastern portion of Lake Michigan–Huron, having the same surface elevation as Lake Michigan, to which it is connected by the 5-mile-wide (8.0 km), 20-fathom-deep (120 ft; 37 m) Straits of Mackinac. Combined, Lake Michigan–Huron is the largest freshwater lake by area in the world. The Huronian glaciation was named from evidence collected from the Lake Huron region. The northern parts of the lake include the North Channel and Georgian Bay. Saginaw Bay is located in the southwest corner of the lake. The main inlet is the St. Marys River from Lake Superior, and the main outlet is through the St. Clair River toward Lake Erie. Lake Huron has a fairly large drainage basin covering parts of Michigan and Ontario. Water flows through Lake Huron faster than the other Great Lakes with a retention time of only 22 years.