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 lakes connect to the Atlantic Ocean via the Saint Lawrence River, and 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 , 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, Buffalo, Cleveland, Detroit, Chicago, and Milwaukee; and, on the Canadian side, Toronto, Hamilton and Mississauga.

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 UK 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

As 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 Chicago River and Calumet River systems connect the Great Lakes Basin to the Mississippi River System through human-made alterations and canals.
* 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.

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 is a large bay on the north shore of Lake Superior bordered to the east by the Sibley Peninsula in northern Ontario.
* 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.
* Thunder Bay is a bay on the west side of Lake Huron in Michigan.
* 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

Although the Saint Lawrence Seaway and Great Lakes Waterway make the Great Lakes accessible to ocean-going vessels, shifts in shipping to wider ocean-going container ships—which do not fit through the locks on these routes—have limited container shipping on the lakes. Most Great Lakes trade is of bulk material, and bulk freighters of Seawaymax-size or less can move throughout the entire lakes and out to the Atlantic. Larger ships are confined to working within the lakes. Only barges can access the Illinois Waterway system providing access to the Gulf of Mexico via the Mississippi River. Despite their vast size, large sections of the Great Lakes freeze over in winter, interrupting most shipping from January to March. Some icebreakers ply the lakes, keeping the shipping lanes open through other periods of ice on the lakes.

The Great Lakes are connected by the Chicago Sanitary and Ship Canal to the Gulf of Mexico via the Illinois River (from the Chicago River) and the Mississippi River. An alternate track is via the Illinois River (from Chicago), to the Mississippi, up the Ohio, and then through the Tennessee–Tombigbee Waterway (a combination of a series of rivers and lakes and canals), to Mobile Bay and the Gulf of Mexico. Commercial tug-and-barge traffic on these waterways is heavy.

Pleasure boats can enter or exit the Great Lakes by way of the Erie Canal and Hudson River in New York. The Erie Canal connects to the Great Lakes at the east end of Lake Erie (at Buffalo, New York) and at the south side of Lake Ontario (at Oswego, New York).

Water levels

The lakes were originally fed by both precipitation and meltwater from glaciers which are no longer present. In modern times, only about 1% of volume per year is "new" water, originating from rivers, precipitation, and groundwater springs. In the post-glacial period, evaporation, and drainage have generally been balanced, making the levels of the lakes relatively constant.

Intensive human population growth began in the region in the 20th century and continues today. At least two human water use activities have been identified as having the potential to affect the lakes' levels: diversion (the transfer of water to other watersheds) and consumption (substantially done today by the use of lake water to power and cool electric generation plants, resulting in evaporation). Outflows through the Chicago Sanitary and Ship Canal is more than balanced by artificial inflows via the Ogoki River and Long Lake/ Kenogami River diversions. Fluctuation of the water levels in the lakes has been observed since records began in 1918. The water level of Lake Michigan–Huron had remained fairly constant over the 20th century. Recent lake levels include record low levels in 2013 in Lakes Superior, Erie, and Michigan-Huron, followed by record high levels in 2020 in the same lakes. The water level in Lake Ontario has remained relatively constant in the same time period, hovering around the historical average level.

Although "true tides—changes in water level caused by the gravitational forces of the sun and moon—do occur in a semi-diurnal (twice daily) pattern", such changes are quite small and generally obscured by other forces. The lake levels are affected primarily by changes in regional meteorology and climatology. The outflows from Lakes Superior and Ontario are regulated, while the outflows of Michigan-Huron and Erie are not regulated at all. Ontario is the most tightly regulated, with its outflow controlled by the Moses-Saunders Power Dam, which explains its consistent historical levels.

Ice cover

The annual ice coverage on the Great Lakes varies greatly from year to year due to weather patterns and long-term climate trends. Ice typically begins forming in December and reaches its peak in February or early March. The extent of ice cover can vary from as little as 10% to over 90% depending on winter severity. For example, during the particularly cold winter of 2013–2014, ice coverage peaked at over 92% across the five lakes, while in milder years like 2023–2024, coverage remained below 20%. Long-term data from the National Oceanic and Atmospheric Administration's Great Lakes Environmental Research Laboratory (NOAA GLERL) indicate a general decline in maximum ice cover over the past few decades, aligning with broader patterns of warming in the region.

Etymology

;Lake Erie
: From the Erie tribe, a shortened form of the Iroquoian word 'long tail'.
; Lake Huron
:Named for the inhabitants of the area, the Wyandot (or "Hurons"), by the first French explorers .. The Wyandot originally referred to the lake by the name , a word which has been variously translated as "Freshwater Sea", "Lake of the Hurons", or simply "lake".
;Lake Michigan
: From the Ojibwe word "great water" or "large lake".
;Lake Ontario
: From the Wyandot word "lake of shining waters".
; Lake Superior
: English translation of the French term "upper lake", referring to its position north of Lake Huron. The indigenous Ojibwe call it (from Ojibwe "big, large, great"; "water, lake, sea"). Popularized in French-influenced transliteration as ''Gitchigumi'' as in Gordon Lightfoot's 1976 story song " The Wreck of the ''Edmund Fitzgerald''", or ''Gitchee Gumee'' as in Henry Wadsworth Longfellow's 1855 epic poem, '' The Song of Hiawatha'').

Statistics

The Great Lakes contain 21% of the world's surface fresh water: , or 6.0×10¹⁵ U.S. gallons, that is 6 quadrillion U.S. gallons, (2.3×10¹⁶ liters). The lakes contain about 84% of the surface freshwater of North America; if the water were evenly distributed over the entire continent's land area, it would reach a depth of 5 feet (1.5 meters). This is enough water to cover the 48 contiguous U.S. states to a uniform depth of . Although the lakes contain a large percentage of the world's fresh water, the Great Lakes supply only a small portion of U.S. drinking water on a national basis.

The total surface area of the lakes is approximately —nearly the same size as the United Kingdom, and larger than the U.S. states of New York, New Jersey, Connecticut, Rhode Island, Massachusetts, Vermont, and New Hampshire combined. The Great Lakes coast measures approximately , but the length of a coastline is impossible to measure exactly. Canada borders approximately of coastline, while the remaining are bordered by the United States. Michigan has the longest shoreline of the United States, bordering roughly of lakes, followed by Wisconsin (), New York (), and Ohio (). Traversing the shoreline of all the lakes would cover a distance roughly equivalent to travelling half-way around the world at the equator.

A notable modern phenomenon is the formation of ice volcanoes over the lakes during wintertime. Storm-generated waves carve the lakes' ice sheet and create conical mounds through the eruption of water and slush. The process is only well-documented in the Great Lakes, and has been credited with sparing the southern shorelines from worse rocky erosion.

Geology

It has been estimated that the foundational geology that created the conditions shaping the present day upper Great Lakes was laid from 1.1 to 1.2 billion years ago, when two previously fused tectonic plates split apart and created the Midcontinent Rift, which crossed the Great Lakes Tectonic Zone. A valley was formed providing a basin that eventually became modern day Lake Superior. When a second fault line, the Saint Lawrence rift, formed approximately 570 million years ago, the basis for Lakes Ontario and Erie was created, along with what would become the Saint Lawrence River.

The Great Lakes are estimated to have been formed at the end of the Last Glacial Period (the Wisconsin glaciation ended 10,000 to 12,000 years ago), when the Laurentide Ice Sheet receded. The retreat of the ice sheet left behind a large amount of meltwater ( Lake Algonquin, Lake Chicago, Glacial Lake Iroquois, and Champlain Sea) that filled up the basins that the glaciers had carved, thus creating the Great Lakes as they are today. Because of the uneven nature of glacier erosion, some higher hills became Great Lakes islands. The Niagara Escarpment follows the contour of the Great Lakes between New York and Wisconsin. Land below the glaciers "rebounded" as it was uncovered. Since the glaciers covered some areas longer than others, this glacial rebound occurred at different rates.

Climate

The Great Lakes have a humid continental climate,
Köppen climate classification Dfa (in southern areas) and Dfb (in northern parts) with varying influences from air masses from other regions including dry, cold Arctic systems, mild Pacific air masses from the west, and warm, wet tropical systems from the south and the Gulf of Mexico. The lakes have a moderating effect on the climate; they can also increase precipitation totals and produce lake effect snowfall.

Lake effect

The Great Lakes can have an effect on regional weather called ''lake-effect snow'', which is sometimes very localized. Even late in winter, the lakes often have no icepack in the middle. The prevailing winds from the west pick up the air and moisture from the lake surface, which is slightly warmer in relation to the cold surface winds above. As the slightly warmer, moist air passes over the colder land surface, the moisture often produces concentrated, heavy snowfall that sets up in bands or "streamers". This is similar to the effect of warmer air dropping snow as it passes over mountain ranges. During freezing weather with high winds, the " snowbelts" receive regular snow fall from this localized weather pattern, especially along the eastern shores of the lakes. Snowbelts are found in Wisconsin, Indiana, Michigan, Ohio, Pennsylvania, New York, and Ontario. Related to the lake effect is the regular occurrence of fog, particularly along the shorelines of the lakes. This is most noticeable along Lake Superior's shores.

The lakes tend to moderate seasonal temperatures to some degree but not with as large an influence as do large oceans; they absorb heat and cool the air in summer, then slowly radiate that heat in autumn. They protect against frost during transitional weather and keep the summertime temperatures cooler than further inland. This effect can be very localized and overridden by offshore wind patterns. This temperature buffering produces areas known as " fruit belts", where fruit can be produced that is typically grown much farther south. For instance, western Michigan has apple orchards, and cherry orchards are cultivated adjacent to the lake shore as far north as the Grand Traverse Bay. Near Collingwood, Ontario, commercial fruit orchards, including a few wineries, exist near the shoreline of southern Nottawasaga Bay. The eastern shore of Lake Michigan and the southern shore of Lake Erie have many successful wineries because of the lakes' moderating effects, as do the large commercial fruit and wine growing areas of the Niagara Peninsula located between Lake Erie and Lake Ontario. A similar phenomenon allows wineries to flourish in the Finger Lakes region of New York, as well as in Prince Edward County, Ontario, on Lake Ontario's northeast shore.

The Great Lakes have been observed to help intensify storms, such as Hurricane Hazel in 1954, and the 2011 Goderich, Ontario tornado, which moved onshore as a tornadic waterspout. In 1996, a rare tropical or subtropical storm was observed forming in Lake Huron, dubbed the 1996 Lake Huron cyclone. Rather large severe thunderstorms covering wide areas are well known in the Great Lakes during mid-summer; these Mesoscale convective complexes or MCCs can cause damage to wide swaths of forest and shatter glass in city buildings. These storms mainly occur during the night, and the systems sometimes have small embedded tornadoes, but more often straight-line winds accompanied by intense lightning.

Ecology

Historically, the Great Lakes, in addition to their lake ecology, were surrounded by various forest ecoregions (except in a relatively small area of southeast Lake Michigan where savanna or prairie occasionally intruded). Logging, urbanization, and agriculture uses have changed that relationship. In the early 21st century, Lake Superior's shores are 91% forested, Lake Huron 68%, Lake Ontario 49%, Lake Michigan 41%, and Lake Erie, where logging and urbanization has been most extensive, 21%. Some of these forests are second or third growth (i.e. they have been logged before, changing their composition). At least 13 wildlife species are documented as becoming extinct since the arrival of Europeans, and many more are threatened or endangered. Meanwhile, exotic and invasive species have also been introduced.

Fauna

While the organisms living on the bottom of shallow waters are similar to those found in smaller lakes, the deep waters contain organisms found only in deep, cold lakes of the northern latitudes. These include the delicate opossum shrimp (order mysida), the deepwater scud (a crustacean of the order amphipoda), two types of copepods, and the deepwater sculpin (a spiny, large-headed fish).

The Great Lakes are an important source of fishing. Early European settlers were astounded by both the variety and quantity of fish; there were 150 different species in the Great Lakes. Throughout history, fish populations were the early indicator of the condition of the Lakes and have remained one of the key indicators even in the current era of sophisticated analyses and measuring instruments. According to the bi-national (U.S. and Canadian) resource book, ''The Great Lakes: An Environmental Atlas and Resource Book'': "The largest Great Lakes fish harvests were recorded in 1889 and 1899 at some 47 million pounds" Bi-national (U.S. and Canadian) resource book.

By 1801, the New York Legislature found it necessary to pass regulations curtailing obstructions to the natural migrations of Atlantic salmon from Lake Erie into their spawning channels. In the early 19th century, the government of Upper Canada found it necessary to introduce similar legislation prohibiting the use of weirs and nets at the mouths of Lake Ontario's tributaries. Other protective legislation was passed, but enforcement remained difficult.

On both sides of the Canada–United States border, the proliferation of dams and impoundments have multiplied, necessitating more regulatory efforts. Concerns by the mid-19th century included obstructions in the rivers which prevented salmon and lake sturgeon from reaching their spawning grounds. The Wisconsin Fisheries Commission noted a reduction of roughly 25% in general fish harvests by 1875. The states have removed dams from rivers where necessary.

Overfishing has been cited as a possible reason for a decrease in population of various whitefish, important because of their culinary desirability and, hence, economic consequence. Moreover, between 1879 and 1899, reported whitefish harvests declined from some 24.3 million pounds (11 million kg) to just over 9 million pounds (4 million kg). By 1900, commercial fishermen on Lake Michigan were hauling in an average of 41 million pounds of fish annually. By 1938, Wisconsin's commercial fishing operations were motorized and mechanized, generating jobs for more than 2,000 workers, and hauling 14 million pounds per year. The population of giant freshwater mussels was eliminated as the mussels were harvested for use as buttons by early Great Lakes entrepreneurs.

''The Great Lakes: An Environmental Atlas and Resource Book'' (1972) notes: "Only pockets remain of the once large commercial fishery." Water quality improvements realized during the 1970s and 1980s, combined with successful salmonid stocking programs, have enabled the growth of a large recreational fishery. The last commercial fisherman left Milwaukee in 2011 because of overfishing and anthropogenic changes to the biosphere.

Invasive species

Since the 19th century, an estimated 160 new species have found their way into the Great Lakes ecosystem; many have become invasive; the overseas ship ballast and ship hull parasitism are causing severe economic and ecological impacts. According to the Inland Seas Education Association, on average a new species enters the Great Lakes every eight months. Introductions into the Great Lakes include the zebra mussel, which was first discovered in 1988, and quagga mussel in 1989. Since 2000, the invasive quagga mussel has smothered the bottom of Lake Michigan almost from shore to shore, and their numbers are estimated at 900 trillion. The mollusks are efficient filter feeders, competing with native mussels and reducing available food and spawning grounds for fish. In addition, the mussels may be a nuisance to industries by clogging pipes. The U.S. Fish and Wildlife Service estimated in 2007 that the economic impact of the zebra mussel could be about $5 billion over the next decade. The state of Michigan has had to develop legislation and regulations to help protect against these invasive species. Aquatic invasive species regulations in Michigan have been put in place to combat the influx of species.

The alewife first entered the system west of Lake Ontario via 19th-century canals. By the 1960s, the small silver fish had become a familiar nuisance to beach goers across Lakes Michigan, Huron, and Erie. Periodic mass die-offs result in vast numbers of the fish washing up on shore; estimates by various governments have placed the percentage of Lake Michigan's biomass which was made up of alewives in the early 1960s as high as 90%. In the late 1960s, the various state and federal governments began stocking several species of salmonids, including the native lake trout as well as non-native chinook and coho salmon; by the 1980s, alewife populations had dropped drastically. The ruffe, a small percid fish from Eurasia, became the most abundant fish species in Lake Superior's Saint Louis River within five years of its detection in 1986. Its range, which has expanded to Lake Huron, poses a significant threat to the lower lake fishery. Five years after first being observed in the St. Clair River, the round goby can now be found in all of the Great Lakes. The goby is considered undesirable for several reasons: it preys upon bottom-feeding fish, overruns optimal habitat, spawns multiple times a season, and can survive poor water quality conditions.

The influx of parasitic lamprey populations after the development of the Erie Canal and the much later Welland Canal led to the two federal governments of the United States and Canada working on joint proposals to control it. By the mid-1950s, the lake trout populations of Lakes Michigan and Huron were reduced, with the lamprey deemed largely to blame. This led to the launch of the bi-national Great Lakes Fishery Commission.

Several species of exotic water fleas have accidentally been introduced into the Great Lakes, such as the spiny waterflea, '' Bythotrephes longimanus'', and the fishhook waterflea, '' Cercopagis pengoi'', potentially having an effect on the zooplankton population. Several species of crayfish have also been introduced that may contend with native crayfish populations. More recently an electric fence has been set up across the Chicago Sanitary and Ship Canal in order to keep several species of invasive Asian carp out of the lakes. These fast-growing planktivorous fish have heavily colonized the Mississippi and Illinois river systems. Invasive species, particularly zebra and quagga mussels, may be at least partially responsible for the collapse of the deepwater demersal fish community in Lake Huron, as well as drastic unprecedented changes in the zooplankton community of the lake.

Microbiology

Scientists understand that the micro-aquatic life of the lakes is abundant but know very little about some of the most plentiful microbes and their environmental effects in the Great Lakes. Although a drop of lake water may contain 1 million bacteria cells and 10 million viruses, only since 2012 has there been a long-term study of the lakes' micro-organisms. Between 2012 and 2019 more than 160 new species have been discovered.

Flora

Native habitats and ecoregions in the Great Lakes region include:

* Alvar
* Boreal rich fen (such as in Door County)
* Eastern forest-boreal transition
* Eastern Great Lakes lowland forests
* Southern Great Lakes forests
* Central forest-grasslands transition
* Upper Midwest forest-savanna transition
* Western Great Lakes forests
* Central Canadian Shield forests
* Laurentian Mixed Forest Province
* Beech-maple forest
* Habitats of the Indiana Dunes

Plant lists include:
* List of Michigan flowers
* List of Minnesota wild flowers
* List of Minnesota trees

Logging

Logging

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