Shaped a bit like a human ear—its name roughly means “ear pendant” in French— Lake Pend Oreille lies in the Idaho panhandle. Carved out by glaciers during the last ice age, it may have been partially filled by a series of mega floods that tore across the Pacific Northwest many thousands of years ago following repeated ruptures of a massive ice dam in the area.

During World War II, the U.S. Navy operated one of the country’s largest naval training centers there, and to this day the Navy uses the deep and quiet waters of the lake to conduct submarine experiments. Lake Pend Oreille is also known for its big fish, including a 37-pound rainbow trout caught in 1947 and a 32-pound bull trout caught in 1949. Moreover, myth holds that the Pend Oreille Paddler, a water creature akin to the Loch Ness Monster, calls the lake home.

Like all the lakes on this list, Pend Oreille struggles with some environmental problems, including pollution and invasive species.

When glaciers plowed through the upper Midwest during the last ice age, they fashioned the region’s soft rock into huge basins that then filled with water as the ice retreated. The five Great Lakes “are sometimes called a gift from the glaciers,” says Joel Brammeier, president and CEO at Alliance for the Great Lakes, an environmental nonprofit.

Lake Superior, the northernmost and westernmost of the Great Lakes, also happens to be the biggest, deepest, coldest, and cleanest. It’s the only Great Lake that’s over 1,000 feet deep (though Lake Michigan comes close at 925 feet deep.) It holds about 10 percent of the world’s fresh surface water, more than all the other Great Lakes combined. And it covers a surface area of around 31,700 square miles, more than any other lake in the world except the Caspian Sea. Lake Superior is so vast, in fact, that the sun reportedly sets about 35 minutes later on its western shore than it does on its southeastern shore.

Fed by hundreds of rivers and streams, Lake Superior’s waters flow slowly through the other Great Lakes and out to the Atlantic Ocean. Thanks to the construction of the Great Lakes-St. Lawrence Seaway System, cargo vessels can follow the path of the water and journey more than 2,000 miles from Duluth, Minnesota, the site of North America’s farthest-inland freshwater seaport, to the Atlantic.

Like the other Great Lakes, Superior suffered in the past from overfishing and contamination from mining, aluminum smelting, paper milling, and other industrial activities. But because of its relative remoteness, its water remained fairly clean and its biodiversity well preserved, according to Brammeier. “The fisheries did not sustain as much damage as the fisheries in the other four Great Lakes,” Brammeier says, pointing out that only Superior maintained a self-sustaining lake trout population.

He says that Superior is warming faster than the other Great Lakes and that algae blooms are starting to appear. Nonetheless, he is heartened by the bipartisan support for the Great Lakes, including the federal Great Lakes Restoration Initiative, which funds toxic chemical cleanups, habitat restorations, and invasive species removals, among other things.

“The awareness and love for the Great Lakes is greater than I’ve ever seen in my life,” Brammeier says. “There is an appreciation of how important these waters are for the surrounding communities, and there’s an understanding that increasing pollution in the Great Lakes is unacceptable.”

Another glacial lake, Washington's Lake Chelan was shaped by one ice sheet moving down from the northwest as a second ice sheet moved up from the southeast. “These two tongues of ice met somewhere in the middle,” says Philip E. Long, director of the nonprofit Lake Chelan Research Institute. He points out that the drop-off from the top of the surrounding peaks to the bottom of the lake is considered “one of the deepest gorges in North America.”

Extremely skinny—Lake Chelan is 50.5 miles long and only two miles wide at its widest point—the waterbody resembles a fjord and acts almost like a slow-moving river, Long explains. The area’s indigenous tribes apparently knew about its exceptional depth. In fact, Chelan is thought to be an anglicized version of the Salish word for “deep water.”

The top of the lake, near North Cascades National Park, is forested, remote, and largely off limits to development, whereas the bottom portion is surrounded by apple orchards, wineries, and vacation homes, along with a hydroelectric dam that raised the level of the lake by about 20 feet when it was constructed nearly 100 years ago.

Long says the lake faces increasing pressures from housing development, wildfires, motor boats, nearshore algae growth and rising populations of Canada geese and non-native Asian clams. According to Long, the lake is also recovering from past logging and mining activity—in one bay, old sunken logs still litter the lake floor—and from past use of the pesticide DDT, which can still be found in extremely high concentrations in Chelan’s lake trout.

Nonetheless, like many of the deepest U.S. lakes, Chelan remains relatively pristine and stable. “It’s the water clarity and the quality of the water that’s most amazing to people when they come here,” Long says.

A major tourist destination for hikers, cyclists, boaters, skiers and swimmers, Lake Tahoe lies nestled within the Sierra Nevada mountains along the border of California and Nevada. Outside of Lake Superior, it’s the largest lake on this list, covering a surface area of about 191 square miles and containing some 39 trillion gallons of water. (In fact, it’s sometimes referred to as the largest alpine lake in North America.) Sixty-three streams flow into the lake and only one flows out.

Formed some 2 million years ago by tectonic movements and volcanic activity, Lake Tahoe has since been further shaped by erosion, earthquakes and glaciers. About 50,000 years ago, for example, an earthquake triggered an underwater landslide that carved out what’s now known as McKinney Bay.

“If you look at the shape of Lake Tahoe, it looks like someone took a bite out of the west side,” says Heather Segale, education and outreach director at the UC Davis Tahoe Environmental Research Center.

She notes that, on certain trails, mountain bikers get a tacit geology lesson. “It’s all shale, and you can hear the sound of the shale clinking,” Segale says. “It sounds like you’re riding on glass.”

Known for its clarity, visitors could at one point see more than 100 feet down. From the 1960s to the 1990s, Tahoe lost about one foot of clarity per year, according to Segale. Luckily, the clarity has since leveled off at around 70 feet, thanks largely to stream and wetland restorations, as well as rules that require landowners to limit the amount of sediment and fine particles that run off their property into the lake.

In recent years, climate change has taken a toll, exacerbating droughts and wildfires, raising water temperatures, and limiting the amount of snowfall, Segale explains. Meanwhile, the introduction of Asian clams has stimulated nearshore algae blooms.

Yet Segale also notes that a cadre of conservationists and scientists are working to Keep Tahoe Blue (as the popular slogan goes). “If we can’t fix it here," says Segale, "then we can’t fix it anywhere."

A relative youngster among U.S. waterbodies, Crater Lake formed around 7,700 years ago when Mount Mazama, a volcano in the Cascade Range in Oregon, exploded so powerfully that it collapsed in on itself, forming a caldera that then filled with rain and snowmelt. “The volcano blew its top, and then what’s left behind is the deep [recess] that made the lake,” Segale says.

Now protected by an eponymous national park, Crater Lake is known for its deep-blue color. With an undeveloped shoreline and a ban on private boats, it’s even clearer than Lake Tahoe, Segale says. Wizard Island, a volcanic cinder cone, extends 763 feet above the lake’s surface.

Yet, even at Crater Lake, environmental challenges have arisen. The proliferation of non-native crayfish, for example, has decimated populations of the Mazama newt—which lives nowhere else on earth—and has also led to increased algae growth. And since 1965, summer surface water temperatures have increased by 5.6 degrees Fahrenheit, scientists have found.

With no streams running in or out, Crater Lake contained no fish when white Americans first arrived. (It has since been stocked with trout and salmon.) In 1886, U.S. geologists, using nothing more than a lead pipe attached to a piano wire as a sounding apparatus, calculated the maximum depth of the lake as 1,996 feet. Later measurements taken with multibeam sidescan sonar confirmed that they were only 53 feet off.

Crater Lake is so cavernous at its deepest point that the Eiffel Tower, the Washington Monument, and the Statue of Liberty—all standing on top of each other—wouldn’t reach the surface.

Still, despite being around the ninth-deepest lake in the world, it pales in comparison to the world’s deepest lake: Lake Baikal in Russia. That lake, which contains about 20 percent of the world’s fresh surface water, is about 5,600 feet deep.