Lakes are formed in a variety of ways. Some lakes were made when ancient glaciers melted. Other lakes were made when the earth's crust shifted to form natural basins. Fiery volcanoes even created some lakes. We all know one when we see it, but what, exactly, is a lake? According to National Geographic, a lake is a body of fresh water or saltwater that is entirely surrounded by land. Smaller lakes may be called ponds, while the biggest lakes on earth are generally referred to as seas. With thousands of lakes and ponds in the U.S., you may be wondering which are the seven largest lakes in the land. Here's what we found out:

Lake of the Woods

Aerial photo of Lake of the Woods
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With around 15,700,000 acre-feet of water, the seventh-largest lake in the U.S. also happens to be one of the biggest lakes in Canada. Spanning the borders between Minnesota, Manitoba, and Ontario, glacier-created Lake of the Woods comprises more than 25,000 miles of shoreline. This enormous American lake boasts the longest lake shoreline in the world, explains Lakelubbers magazine.

The westernmost section of Lake of the Woods is mainly open water. More easterly parts of the lake are peppered with thousands of small islands that are home to moose, bald eagles, bear, and other Minnesota wildlife.

In the summertime, fishers flock to the blue waters of Lake of the Woods to catch record-setting walleye, small-mouth bass, lake sturgeon, perch, and muskie. During winter months, Lake of the Woods transforms into a cold-weather playground replete with ice fishing, snowshoeing, cross-country skiing, and snowball fights.

Great Salt Lake

Photo of Great Salt Lake at sunrise
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Comprising some 28 million acre-feet of saline water, Utah's Great Salt Lake claims the title of the sixth-largest lake in the U.S. It's also the second-largest lake that sits completely within United States borders.

The most significant remaining vestige of a prehistoric 1,000-foot-deep lake known as Lake Bonneville, the Great Salt Lake lives up to its name with water that is significantly saltier than the other lakes in this list.

The Great Salt Lake is home to a protected pelican rookery as well as a several small islands that are populated with American bison, bighorn sheep, pronghorn antelope, and numerous shorebirds and waterfowl, including avocets, swans, ducks, and gulls. Due to its high salt levels, nothing but brine shrimp and algae live in the lake water, according to Lakelubbers.

Lake Ontario

Photo of Lake Ontario at sunset
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With roughly 1,328,025,600 acre-feet of freshwater, Lake Ontario is the smallest of the Great Lakes but ranks as the fifth-biggest lake in the United States as well as the 14th-largest lake in the world. It's not all in the U.S., however. Formed by glacial activity long ago, Lake Ontario shorelines meander through Canada and New York.

Fed primarily by the Niagara River by way of Lake Erie, Lake Ontario ultimately flows into the St. Lawrence River. Water that evaporates from Lake Erie typically returns in the form of snow that falls on northern New York State, according to Lakelubbers.

At 802 feet, Ontario is the second-deepest of the Great Lakes. The scenic lake offers more than 700 miles of hike-able shoreline and plentiful fishing opportunities. Angler favorites include brown trout, black bass, brown trout, coho and king salmon, lake trout, perch, spring kings, walleye, and steelhead.

Lake Erie

Photo of Lake Erie under clouds
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With a relatively mere 391,987,200 acre-feet of water, Erie is the southernmost and smallest by volume of the five Great Lakes as well as the fourth-largest lake in the U.S. Straddling the boundaries of Ontario, Michigan, New York, Pennsylvania, and Ohio, Lake Erie is the shallowest of the Great Lakes.

Because Erie has an average depth of just 62 feet, it is the only one of the Great Lakes to freeze over intermittently. In the wintertime, ice fishing is a big deal in Lake Erie where daring anglers brave the elements to pull walleye, yellow perch, steelhead, salmon, and small-mouth bass through holes bored in the ice.

Nobody knows exactly how many islands are in Lake Erie, but Lakelubbers says that there are at least 36 inhabited and abandoned islands, including Buckeye, Catawba, Gibraltar, Kafralu, Middle Bass, Mouse, and West Sister Island.

Lake Michigan

Photo of Lake Michigan shoreline
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Comprising 3,987,456,000 acre-feet of fresh water, Lake Michigan is the only one of the Great Lakes to sit entirely within United States boundaries. With 1,640 miles of shoreline in Michigan, Wisconsin, Illinois, and Indiana, Lake Michigan also happens to have the biggest surface area of any single-country freshwater lake.

If you think the only wine country in America is on the west coast, you may be surprised to learn that the Lake Michigan Shore is a designated American Viticultural Area with hundreds of wineries that make wine from cool weather-loving Riesling grapes.

Lake Huron

Photo of Lake Huron at sunset
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With a basin that holds 850 cubic miles of water, Lake Huron ranks as the second-largest lake in the U.S. Nearly 4,000 miles of rocky shoreline and sandy beaches make Huron a popular Midwest vacation spot.

Visitors to Lake Huron's Mackinac Island State Park experience a step back in time. The park allows no automobiles or motorcycles, but offers ample opportunity to bike, walk, or catch a ride on a horse-drawn carriage, explains Lakelubbers. A quaint village and exceptional bird watching are additional features enjoyed by visitors to this historic island.

In the summertime, fishermen (and women) flock to the shore at Saginaw Bay to angle for record-breaking walleye. Year-round fishing is good here, too, with plentiful musky, trout, bass, and salmon.

Lake Superior

Photo of Lake Superior in winter with a lighthouse in the background
Credit: Dennis O'Hara/ Shutterstock

Superlative in several ways, the largest lake in the U.S. boasts a whopping 9,799,680,000 acre-feet of freshwater. This astounding number represents 400,000 gallons of water for every woman, man, and child on the planet, explains Lakelubbers.

Not only is Lake Superior the biggest lake in the U.S., but it's also the cleanest, coldest, and deepest of the five Great Lakes. When measured by surface area, Superior is the largest freshwater lake in the entire world.