Hidden depths
America’s lost ocean: How the Great Lakes came to be
Image: Randy Laybourne
Like legendary giants, the Great Lakes are North America's watery core, influencing commerce, climate, and culture. Stretching across the U.S. and Canada, these five immense lakes—Superior, Michigan, Huron, Erie, and Ontario—contain an astounding 84% of North America's fresh surface water. Here are 11 fascinating facts about these monumental lakes that may have flown under your radar until now.
1
Lake Superior lives up to its name
Image: Jacob Skowronek
Lake Superior is the largest, deepest, and coldest of the five. It holds more water than the other four lakes combined—enough to cover North and South America in a foot of water. At 31,700 square miles, it’s the largest freshwater lake by surface area in the world.
2
Only one is fully American
Image: Ioann-Mark Kuznietsov
Lake Michigan is the only Great Lake entirely within the jurisdiction of the United States. It touches four states—Wisconsin, Illinois, Indiana, and Michigan—and its shores are home to major cities like Chicago and Milwaukee. As if this wasn’t enough, this lake also boasts the world’s largest freshwater sand dunes.
3
They create their own weather
Image: Srikanta H. U
The Great Lakes have a powerful influence on regional weather, especially through the phenomenon of "lake-effect snow." As cold air sweeps over the warmer lakes, it picks up moisture, resulting in heavy snowfall in cities like Buffalo, Cleveland, and Chicago. The lakes also generate localized storms that can rival oceanic tempests in intensity. Yet, not all is harsh; these unique conditions help create microclimates that are perfect for agriculture, supporting a range of crops across the region.
4
A shipwreck graveyard
Image: Vlad Tchompalov
Prone to stormy and unpredictable weather, the Great Lakes are home to over 6,000 shipwrecks. The most infamous of these, the SS Edmund Fitzgerald, sank in Lake Superior during a violent storm in 1975, inspiring Gordon Lightfoot's iconic ballad. In fact, many of these wrecks are remarkably well-preserved, thanks to the cold freshwater, which slows down the decay process and keeps these sunken ships intact for decades.
5
They contain a fifth of the world’s freshwater
Image: Sime Basioli
The Great Lakes hold about 21% of the world's fresh surface water. That’s roughly six quadrillion gallons—enough to submerge the lower 48 states under about 10 feet of water. Given this staggering quantity, it's no surprise that the lakes are crucial to American drinking water, agriculture, and industry.
6
The Erie Canal’s role
Image: Lucy M
Opened in 1825, the Erie Canal linked the Great Lakes to the Atlantic Ocean via the Hudson River, transforming trade and settlement patterns. It played a pivotal role in making New York City an economic powerhouse and significantly accelerated the movement of goods between the Midwest and the East Coast. While most traffic now flows through the larger St. Lawrence Seaway, the Erie Canal remains a key chapter in U.S. history.
7
When the Niagara Falls stood still
Image: Vishwesh Jirgale
In 1969, engineers temporarily halted the flow of Niagara Falls due to concerns that erosion was progressing so rapidly the falls could disappear in a few years. After a thorough inspection by the Army Corps of Engineers, they concluded that no immediate maintenance was necessary. Despite this, the endeavor was far from futile—it provided valuable insights that would guide future preservation efforts for the iconic falls.
8
America’s forgotten "Third Coast"
Image: Richard Main
The Great Lakes coastline spans about 10,900 miles, which makes it longer than the U.S. East and West Coasts combined. This hidden "Third Coast" features sandy beaches, towering cliffs, and picturesque lighthouses, making it a popular destination for tourism and outdoor recreation.
9
Once an ancient ocean
Image: Andrzej Kryszpiniuk
Millions of years ago, the region now holding the Great Lakes was covered by an ancient sea. Over time, glaciers carved out the massive basins, which filled with meltwater after the Ice Age. The evidence of this transformation is still visible in the region’s fossils and rock formations.
10
Chicago River’s historic reversal
Image: Jake Leonard
In 1900, engineers reversed the flow of the Chicago River to prevent sewage from polluting Lake Michigan, the city’s drinking water source. Using a system of canals, the river was redirected toward the Mississippi River watershed, an astonishing feat of engineering that still works to this day.
11
Protected by an international treaty
Image: Hermes Rivera
The 1909 Boundary Waters Treaty between the U.S. and Canada governs the Great Lakes, ensuring cooperative water management. It led to the creation of the International Joint Commission, which helps both nations resolve disputes and protect this vital natural resource.
