Lake Erie in the context of Niagara Gorge

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.

The Great Lakes Waterway (GLW) is a system of natural channels and artificial locks and canals that enable navigation between the North American Great Lakes. Although all of the lakes are naturally connected as a chain, water travel between the lakes was impeded for centuries by obstacles such as Niagara Falls and the rapids of the St. Marys River.

Its principal civil engineering works are the Welland Canal between Lakes Ontario and Erie, and the Soo Locks between Huron and Superior. Dredged channels were constructed in the St. Marys River, the Detroit River, Lake St. Clair and the St. Clair River between Huron and Erie. Usually, one or more U.S. Coast Guard icebreakers help keep the water passage open for part of the fall and early winter, although shipping usually ceases for two to three months thereafter. The St. Lawrence Seaway allows navigable shipping from the GLW to the Atlantic Ocean, while the Illinois Waterway extends commercial shipping to the Mississippi River and the Gulf of Mexico. The Great Lakes Waterway is co-administered by the governments of Canada and the United States.

Buffalo is a city in the U.S. state of New York. It lies in Western New York at the eastern end of Lake Erie and at the head of the Niagara River on the Canada–United States border. It is the second-most populous city in New York, with a population of 278,349 at the 2020 census. The Buffalo–Niagara Falls metropolitan area, with over 1.16 million residents, is the 51st-largest metropolitan area in the United States. Buffalo is the county seat of Erie County.

Before the 17th century, the region was inhabited by nomadic Paleo-Indians who were succeeded by the Neutral, Erie, and Iroquois nations. In the early 17th century, the French began to explore the region. In the 18th century, Iroquois land surrounding Buffalo Creek was ceded through the Holland Land Purchase, and a small village was established at its headwaters. Buffalo was selected as the terminus of the Erie Canal in 1825, which led to its incorporation in 1832 and stimulated its growth as the primary inland port between the Great Lakes and Atlantic Ocean. Transshipment made Buffalo the world's largest grain port in that era. After the coming of railroads greatly reduced the canal's importance, the city became the second-largest railway hub (after Chicago), and the city came to be dominated by steel production by the 20th century. Later, deindustrialization and the opening of the St. Lawrence Seaway saw the city's economy decline and diversify. It developed its service industries, such as health care, retail, tourism, logistics, and education, while retaining some manufacturing.

Ohio (/oʊˈhaɪ.oʊ/ oh-HY-oh) is a state in the Midwestern region of the United States. It borders Lake Erie to the north, Pennsylvania to the east, West Virginia to the southeast, Kentucky to the southwest, Indiana to the west, and Michigan to the northwest. Of the 50 U.S. states, it is the 34th-largest by area. With a population of nearly 11.9 million, Ohio is the seventh-most populous and tenth-most densely populated state. Its capital and most populous city is Columbus, with other major metropolitan centers including Cleveland and Cincinnati, as well as Dayton, Akron, and Toledo. Ohio is nicknamed the "Buckeye State" after its Ohio buckeye trees, and Ohioans are also known as "Buckeyes".

Ohio derives its name from the Ohio River that forms its southern border, which, in turn, originated from the Seneca word ohiːyo', meaning "good river", "great river", or "large creek". The state was home to several ancient indigenous civilizations, with humans present as early as 10,000 BC. It arose from the lands west of the Appalachian Mountains that were contested by various native tribes and European colonists from the 17th century through the Northwest Indian Wars of the late 18th century. Ohio was partitioned from the Northwest Territory, the first frontier of the new United States, becoming the 17th state admitted to the Union on March 1, 1803, and the first under the Northwest Ordinance. It was the first post-colonial free state admitted to the union and became one of the earliest and most influential industrial powerhouses during the 20th century.

Pennsylvania, officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, Maryland to its south, West Virginia to its southwest, Ohio and the Ohio River to its west, Lake Erie and New York to its north, the Delaware River and New Jersey to its east, and the Canadian province of Ontario to its northwest via Lake Erie. Pennsylvania's most populous city is Philadelphia. The state capital is Harrisburg. Among all states, Pennsylvania is the fifth-most populous with over 13 million residents as of the 2020 United States census, the ninth-highest by population density, and the 33rd-largest by land area. The largest metropolitan statistical area is the southeastern Philadelphia metropolitan area, centered on Philadelphia, the state's most populous and nation's sixth-most populous city. The second-largest metropolitan area, Greater Pittsburgh, is centered in and around Pittsburgh, the state's second-largest city.

Pennsylvania was founded in 1681 through a royal land grant to William Penn, the son of the state's namesake. Before that, between 1638 and 1655, a southeast portion of the state was part of New Sweden, a Swedish colony. Established as a haven for religious and political tolerance, the colonial-era Province of Pennsylvania was known for its relatively peaceful relations with native tribes, innovative government system, and religious pluralism. Pennsylvania played a vital and historic role in the American Revolution and the ultimately successful quest for independence from the British Empire, hosting the First and Second Continental Congress in Philadelphia, the latter of which formed the Continental Army commanded by George Washington in 1775, during the American Revolutionary War, unanimously adopted the Declaration of Independence the following year. On December 12, 1787, Pennsylvania was the second state to ratify the U.S. Constitution, right after Delaware.

Cleveland is a city in the U.S. state of Ohio and the county seat of Cuyahoga County. Located along the southern shore of Lake Erie, it is situated across the Canadian border and approximately 60 mi (97 km) west of the Ohio–Pennsylvania state line. Cleveland is the most populous city on Lake Erie and second-most populous city in Ohio, with a population of 372,624 at the 2020 census. The Cleveland metropolitan area, with an estimated 2.17 million residents, is the 34th-largest metropolitan area in the United States.

Cleveland was founded in 1796 near the mouth of the Cuyahoga River as part of the Connecticut Western Reserve in modern-day Northeast Ohio by General Moses Cleaveland, after whom the city was named. The city's location on the river and the lake shore allowed it to grow into a major commercial and industrial metropolis by the late 19th century, attracting large numbers of immigrants and migrants. It was among the top 10 largest U.S. cities by population for much of the 20th century, a period that saw the development of the city's cultural institutions. By the 1960s, Cleveland's economy began to slow down as manufacturing declined and suburbanization occurred.

The Erie Canal is a historic canal in upstate New York that runs east–west between the Hudson River and Lake Erie. Completed in 1825, the canal was the first navigable waterway connecting the Atlantic Ocean to the upper Great Lakes above Niagara Falls, vastly reducing the costs of transporting people and goods across the Appalachians. The Erie Canal accelerated the settlement of the Great Lakes region, the westward expansion of the United States, and the economic ascendancy of New York state.

A canal from the Hudson River to the Great Lakes was first proposed in the 1780s, but a formal survey was not conducted until 1808. The New York State Legislature authorized construction in 1817. Political opponents of the canal (referencing its lead supporter New York Governor DeWitt Clinton) denigrated the project as "Clinton's Folly" and "Clinton's Big Ditch". Nonetheless, the canal saw quick success upon opening on October 26, 1825, with toll revenue covering the state's construction debt within the first year of operation. The westward connection gave New York City a strong advantage over all other US ports and brought major growth to canal cities such as Albany, Utica, Syracuse, Rochester, and Buffalo.

The geography of New York varies widely across the state. Most of New York is dominated by farms, forests, rivers, mountains, and lakes. New York's Adirondack Park is larger than any U.S. National Park in the contiguous United States. Niagara Falls, on the Niagara River as it flows from Lake Erie to Lake Ontario, is a popular attraction. The Hudson River begins near Lake Tear of the Clouds and flows south through the eastern part of the state without draining lakes George or Champlain. Lake George empties at its north end into Lake Champlain, whose northern end extends into Canada, where it drains into the Richelieu River and then the St. Lawrence. Four of New York City's five boroughs are on the three islands at the mouth of the Hudson River: Manhattan Island, Staten Island, and Brooklyn and Queens on Long Island.

"Upstate" is a common term for New York counties north of suburban Westchester, Rockland and Dutchess counties. Upstate New York typically includes the Catskill Mountains or areas North of the Catskill Mountains, the Capital District, The Adirondacks, the Erie Canal, Lake Champlain, Otsego Lake, Oneida Lake; rivers such as the Delaware, Genesee, Mohawk, and Susquehanna. The highest elevation in New York is Mount Marcy of the Adirondack Mountains. New York is the 27th-largest state.

A harmful algal bloom (HAB), or excessive algae growth, sometimes called a red tide in marine environments, is an algal bloom that causes negative impacts to other organisms by production of natural algae-produced toxins, water deoxygenation, mechanical damage to other organisms, or by other means. HABs are sometimes defined as only those algal blooms that produce toxins, and sometimes as any algal bloom that can result in severely lower oxygen levels in natural waters, killing organisms in marine or fresh waters. Blooms can last from a few days to many months. After the bloom dies, the microbes that decompose the dead algae use up more of the oxygen, generating a "dead zone" which can cause fish die-offs. When these zones cover a large area for an extended period of time, neither fish nor plants are able to survive.

It is sometimes unclear what causes specific HABs as their occurrence in some locations appears to be entirely natural, while in others they appear to be a result of human activities. In certain locations there are links to particular drivers like nutrients, but HABs have also been occurring since before humans started to affect the environment. HABs are induced by eutrophication, which is an overabundance of nutrients in the water. The two most common nutrients are fixed nitrogen (nitrates, ammonia, and urea) and phosphate. The excess nutrients are emitted by agriculture, industrial pollution, excessive fertilizer use in urban/suburban areas, and associated urban runoff. Higher water temperature and low circulation also contribute.

Kelleys Island is both a village in Erie County, Ohio, and the island which it fully occupies in Lake Erie. The island has a total area of 4.41 square miles (11.42 km) and was formed by glacial action on limestone and dolomite.

As of the 2020 census it has a year-round population of under 300 and is primarily a vacation destination with a large seasonal influx of visitors and workers.