Great Lakes

• 1. Introduction

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  The Great Lakes hold more than 20% of the world's surface fresh water by volume. Five interconnected freshwater bodies straddle the Canada-United States border: Superior, Michigan, Huron, Erie, and Ontario. Together they cover roughly 94,250 square miles, nearly the size of the United Kingdom. Their volume, measured at the low water datum, reaches 5,439 cubic miles.

  These are no ordinary lakes. Rolling waves, sustained winds, strong currents, great depths, and distant horizons have earned them an old nickname: inland seas. Sailors who work them speak of boats and lakers and salties, a vocabulary all their own. Storms rise without warning in autumn, and hundreds of ships have gone down beneath the water.

  How did five basins fill with a fifth of the planet's fresh surface water? Why do two of the lakes count as one? What lives in waters cold and deep enough to host creatures found nowhere but the far north? And what happens when 22 million pounds of plastic enter such a system every year? The water flows from Superior down to the Atlantic, and the answers flow with it.

• 2. One Lake In Five

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  Hydrologically, Lakes Michigan and Huron are a single body of water, joined at the Straits of Mackinac. The straits run 5 miles wide and 120 feet deep. Water levels on both sides rise and fall together, and the flow between them frequently reverses direction. Scientists sometimes name the combined body Lake Michigan-Huron.

  Lake Superior sits highest, at 600 feet of elevation, and plunges to a maximum depth of 1,333 feet. Lakes Superior, Huron, Michigan, and Erie all rest at roughly the same elevation, while Lake Ontario lies significantly lower at 246 feet. Because the Niagara Escarpment blocks all natural navigation, the four upper lakes are commonly called the upper great lakes, though the label is not universal.

  Direction itself bends to local custom here. People living on Lake Superior's shore call all the others the lower lakes, because they are farther south. Bulk-freighter sailors hauling cargo toward Erie or Ontario use the same terms, treating those two as down south and the rest as up north. A vessel sailing north on Lake Michigan is considered upbound, even when it moves toward the lake's effluent current.

  Lake Michigan stands apart in one respect: it is the only Great Lake entirely within the United States. The others form a water boundary with Canada. Lake Michigan is also the largest lake by surface area that lies wholly within a single country.

• 3. Carved By Ice

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  Around 1.1 to 1.2 billion years ago, two previously fused tectonic plates split apart and created the Midcontinent Rift, crossing the Great Lakes Tectonic Zone. The valley it formed became the basin of modern Lake Superior. A second fault, the Saint Lawrence rift, formed roughly 570 million years ago and set the stage for Lakes Ontario and Erie, along with the Saint Lawrence River.

  The Wisconsin glaciation ended 10,000 to 12,000 years ago, and as the Laurentide Ice Sheet receded, it left enormous volumes of meltwater behind. Glacial lakes named Algonquin, Chicago, and Iroquois, along with the Champlain Sea, filled the basins the ice had carved. Because glacier erosion was uneven, some higher hills survived as islands. The Niagara Escarpment traces the contour of the lakes between New York and Wisconsin.

  The ice did not release its grip evenly. Land below the glaciers rebounded as it was uncovered, and because some areas stayed buried longer than others, that rebound happened at different rates. Lake Nipigon, north of Superior, sits in a failed arm of a triple junction from the Midcontinent Rift event, an upheaval dated to about 1.1 billion years ago.

• 4. Islands And Inland Seas

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  Roughly 35,000 islands are scattered across the Great Lakes. The largest is Manitoulin Island in Lake Huron, the biggest island in any inland body of water on Earth. Manitoulin is large enough to hold lakes of its own, and its Lake Manitou is the world's largest lake on a freshwater island. Some of those lakes have their own islands, like Treasure Island in Lake Mindemoya. The second-largest is Isle Royale in Lake Superior.

  Green Bay reaches along the south coast of Michigan's Upper Peninsula and the east coast of Wisconsin, separated from the rest of Lake Michigan by the Door and Garden peninsulas and a chain of islands, all formed by the Niagara Escarpment. Georgian Bay extends northeast from Lake Huron entirely within Ontario, walled off by the Bruce Peninsula, Manitoulin Island, and Cockburn Island.

  Grand Traverse Bay ranks among the largest natural harbors in the Great Lakes, split into east and west arms by the Old Mission Peninsula. Its name comes from Jacques Marquette's crossing from Norwood to Northport, which he called La Grande Traversee. Saginaw Bay, reaching into Michigan's Lower Peninsula, holds the largest contiguous freshwater wetland in the United States.

  Then there is Lake St. Clair, joined to Lake Huron by the St. Clair River and to Lake Erie by the Detroit River. It is 17 times smaller in area than Lake Ontario and only rarely listed among the Great Lakes. Yet proposals for its official recognition as a Great Lake are occasionally made.

• 5. Paths To The Sea

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  The St. Marys River, including the Soo Locks, carries Lake Superior's water into Lake Huron by way of the North Channel. From there the St. Clair River feeds Lake St. Clair, the Detroit River feeds Lake Erie, and the Niagara River with its falls drops down to Lake Ontario. The Welland Canal bypasses the Niagara River to make the same connection. Finally the Saint Lawrence River and Seaway carry the water to the Gulf of Saint Lawrence and the Atlantic.

  A second route runs the other way, toward the Gulf of Mexico. The Chicago and Calumet River systems link the Great Lakes Basin to the Mississippi through human-made canals. The Chicago Sanitary and Ship Canal connects to the Gulf via the Illinois and Mississippi rivers, and an alternate track climbs the Ohio and threads the Tennessee-Tombigbee Waterway to Mobile Bay.

  Ocean-going container ships changed the calculus. Wider modern vessels do not fit the locks, so container shipping on the lakes has been limited. Most Great Lakes trade is bulk material, and freighters of Seawaymax size or smaller can move throughout the lakes and out to the Atlantic. Larger ships stay confined within the lakes, while only barges can reach the Illinois Waterway and the Gulf.

  Pleasure boats have their own door east. The Erie Canal and Hudson River connect to Lake Erie at Buffalo, New York, and to Lake Ontario at Oswego. Despite the lakes' size, large sections freeze in winter, interrupting most shipping from January to March until icebreakers reopen the lanes.

• 6. Living Waters

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  Early European settlers were astounded by the fish, both the variety and the quantity, counting 150 different species across the Great Lakes. The deep, cold waters hold organisms found only in the far north: the delicate opossum shrimp, the deepwater scud, two kinds of copepods, and the spiny, large-headed deepwater sculpin. The largest harvests on record came in 1889 and 1899, at some 67,000 tonnes, or 147 million pounds.

  The abundance did not last untouched. As early as 1801, the New York Legislature passed rules to curb obstructions to Atlantic salmon migrating from Lake Erie into spawning channels. Reported whitefish harvests fell from some 24.3 million pounds between 1879 and 1899 to just over 9 million. By 1900, commercial fishermen on Lake Michigan averaged 41 million pounds annually, and by 1938 Wisconsin's motorized operations employed more than 2,000 workers. The last commercial fisherman left Milwaukee in 2011.

  The alewife slipped into the system west of Lake Ontario through 19th-century canals. By the early 1960s these small silver fish may have made up as much as 90% of Lake Michigan's biomass, washing ashore in periodic mass die-offs. In the late 1960s governments began stocking salmonids, including native lake trout and non-native Chinook and coho salmon, and by the 1980s alewife numbers had dropped sharply.

  Parasitic sea lamprey arrived after the Erie and later Welland canals opened. By the mid-1950s the lake trout populations of Michigan and Huron had collapsed, with the lamprey largely blamed, prompting the creation of the bi-national Great Lakes Fishery Commission. Fish populations have long served as the earliest indicator of the lakes' health, a role they still hold.

• 7. Invaders And Contaminants

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  An estimated 160 new species have found their way into the Great Lakes ecosystem since the 19th century, arriving in ship ballast and as hull parasites. The Inland Seas Education Association reports that, on average, a new species enters every eight months. The zebra mussel was first discovered in 1988 and the quagga mussel in 1989. Since 2000 the quagga has smothered the bottom of Lake Michigan nearly shore to shore, with numbers estimated at 900 trillion.

  The round goby spread to all five lakes within five years of first being seen in the St. Clair River. The ruffe, a small Eurasian percid, became the most abundant fish in Lake Superior's Saint Louis River within five years of its 1986 detection. An electric fence now spans the Chicago Sanitary and Ship Canal to keep invasive Asian carp out. The U.S. Fish and Wildlife Service estimated in 2007 that the zebra mussel's economic impact could reach about $5 billion over the following decade.

  Pollution drew its own response. The first U.S. Clean Water Act passed in 1972 over President Richard Nixon's veto, alongside the bi-national Great Lakes Water Quality Agreement. The first of 43 Areas of Concern to be formally de-listed was Ontario's Collingwood Harbour in 1994, with Severn Sound following in 2003. Blue-green algae blooms have troubled Lake Erie since 2011, and the largest to date came in 2015, exceeding the severity index at 10.5.

  Plastic poses a newer threat. More than 22 million pounds enter the lakes each year, breaking into microplastics found in 100 percent of fish studied by the Rochman Lab. Nearly 40 million people in the region rely on the lakes for drinking water. The Great Lakes Plastic Cleanup project captured 74,000 pieces of trash with floating Seabin devices between 2020 and 2021, though it makes no claim of keeping pace.

• 8. Boats And The Boneyards

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  On the 7th of August 1679, a brigantine commissioned by Rene-Robert Cavelier, Sieur de La Salle, became the first known sailing ship to travel the upper Great Lakes. Built at Cayuga Creek near the southern end of the Niagara River, Le Griffon was also the first ship to sink in Lake Michigan, caught in a 1679 storm while trading furs and lost with all hands. A wreck claimed to be hers was reported in 2004 and again, at a different site, in 2014.

  Maritime culture here grew up apart, with its own words. Ships of any size are called boats, lake traders are lakers, and foreign vessels are salties. Since about 1950 a common sight has been the 1,000 by 105 foot self-unloader, a laker with a conveyor belt that swings a crane over the side to empty itself. During World War II, the risk of submarine attacks on coastal training sites led the U.S. Navy to run two aircraft carriers on the lakes as training ships.

  Autumn storms make these waters lethal, especially from late October into early December. The greatest concentration of wrecks lies near Thunder Bay beneath Lake Huron, where shipping lanes converge. The stretch from Grand Marais, Michigan, to Whitefish Point earned the name Graveyard of the Great Lakes. The Whitefish Point Underwater Preserve guards the wrecks as an underwater museum.

  The ore carrier Cyprus, 420 feet long, sank in a Lake Superior storm on the 11th of October 1907, during its second voyage; of 23 crew, only Charles Pitz survived, floating on a life raft for almost seven hours. The French minesweepers Inkerman and Cerisoles vanished in a 1918 Lake Superior blizzard, taking 78 lives in the greatest unexplained loss on the Great Lakes. They remain missing still.