Researchers have found several ancient stone structures beneath the Great Lakes, including a formation in Lake Michigan that resembles Stonehenge. The site, located about 40 feet below the surface, consists of two concentric circles of stones. It is estimated to be over 9,000 years old, which would make it considerably older than the well-known monument in England.
One of the stones bears a carving of a mastodon, an animal that has been extinct for roughly 10,000 years. This suggests the structure was built by people who lived alongside these creatures. At the time the stones were placed, the water level in Lake Michigan was significantly lower than it is today.
Researchers have proposed different explanations for the structure. One theory suggests it served as a hunting trap, with early hunters using the circular formation to herd large animals into a confined space. Another theory holds that the site had spiritual significance. Local Native American communities have indicated that stones are considered living beings in their traditions, and an elder from one community has suggested the formation was placed by ancestors to honor the land.
The underwater location makes the site difficult to study with traditional archaeological tools. Researchers are using newer methods, including 3D modeling, to examine the stones more closely. The work is slow and expensive, and no timeline has been given for when the investigation might be completed.
Lake Michigan has yielded other archaeological finds. The wreck of the Margaret A. Muir, a three-masted schooner built in 1872, was located in May 2024 by the Wisconsin Underwater Archaeological Association. The ship sank on September 30, 1893, after a sudden storm hit while it was carrying salt from Bay City, Michigan, to Chicago. The crew abandoned the ship and reached shore safely. The wreck was found about 50 feet below the surface off the coast of Algoma, Wisconsin, and is reported to be well preserved.
Nearby, in Lake Mendota near Madison, Wisconsin, researchers have found 11 ancient canoes. The oldest is believed to date to around 2,500 BCE. The first canoe was recovered in 2021, and additional canoes have been found since. One theory is that the canoes were intentionally sunk during winter to prevent damage from ice. Historians have suggested that an ancient village may be located under the water, though none has been found so far.
A similar stone formation exists in Lake Constance in Switzerland. Archaeologists discovered a line of 170 man-made stone structures there in 2015. The site dates to around 5,500 years ago, placing it in the same period as the original Stonehenge.
In Lake Huron, researchers have found evidence of human activity dating back about 10,000 years. In 2013, scientists recovered small flakes of obsidian from the lakebed, about 100 feet below the surface. Testing showed the volcanic glass came from central Oregon, roughly 2,500 miles away. The flakes had been shaped by human hands. The find suggests that a trade network spanning the continent existed at the time. The site is located on the Alpena-Amberley Ridge, a submerged landform that once connected Michigan and Ontario. Researchers have also found preserved trees and peat bogs in the area, which have helped preserve organic material for thousands of years.
Other submerged sites around the world include Pavlopetri, an ancient city off the coast of Greece. It is considered the oldest known sunken city, with origins dating back around 5,000 years. Archaeologists have mapped buildings, streets, and tombs beneath about 10 to 13 feet of water. The cause of its submersion is unknown, though some scientists believe an earthquake may be responsible.
The Yonaguni Monument, located off the Ryukyu Islands in Japan, was discovered by a diver in 1986. The structure sits 82 feet underwater and consists of terraced stone platforms that some believe were shaped by human hands. Other geologists argue that the formations are natural, created by tectonic activity and erosion. No consensus has been reached.
Lake Lanier in North Georgia is an artificial lake created in 1956 for flood control, drinking water, and hydroelectric power. The creation of the lake required the displacement of about 700 families. The area had also been home to the Cherokee people until they were removed in the 1830s. A cemetery was left in place and is now submerged. Since the lake was created, hundreds of people have died there in drownings and boating accidents. No scientific evidence links the site’s history to the accident rate, though local legends have developed around the lake. In 1958, two young women drove off a bridge into the lake and disappeared. One body was found a year later, and the car containing the second woman was recovered in 1990.
Northern Ireland’s Loughareema, sometimes called the Vanishing Lake, fills and drains through gaps in its bed. When water levels rise, debris plugs are forced out and the lake drains underground. The process is natural and has been occurring for centuries.
The Mississippi River has reversed its flow on three documented occasions. In the winter of 1811 and 1812, a series of powerful earthquakes struck the New Madrid region. The ground shook over an area far larger than the impact zone of the 1906 San Francisco earthquake. During the largest tremor, on February 7, 1812, the riverbed was pushed upward, blocking the water and causing the river to flow backward temporarily. Islands disappeared, and new lakes formed, including Reelfoot Lake in Tennessee. About a thousand people died, a relatively low number because the region was sparsely populated at the time. The same fault zone is still active, and scientists estimate a 25 to 40 percent chance of a major earthquake in the next 50 years. Much of the region’s infrastructure, including bridges and buildings in Memphis, was not built to withstand strong shaking.
The river reversed again during Hurricane Katrina in 2005, when the storm pushed water inland with enough force to redirect the Mississippi for a period. It happened a third time during Hurricane Isaac in 2012, a Category 1 storm that caused significant flooding and damage along the Gulf Coast.
The wreck of the F.J. King, a 140-foot ship that disappeared in Lake Michigan in 1886, was found in June 2025. The vessel was carrying iron ore from Michigan to Chicago when it was caught in a storm with waves near 10 feet high. The crew abandoned ship and were rescued by a passing schooner. The captain reported the ship went down about five miles offshore, but a lighthouse keeper later spotted the masts closer to shore. The discrepancy was never resolved, and the wreck remained lost for nearly 140 years. A researcher named Brendan Bailod and a team of about 20 scientists and historians used historical documents and new sonar technology to narrow the search area. They found the wreck less than half a mile from where the lighthouse keeper had reported it. The hull was largely intact. The team was testing new side-scan sonar equipment at the time and located the ship after about two hours of searching. The wreck is one of roughly 6,000 ships damaged or destroyed in the Great Lakes during the 1800s.
Fossils of mosasaurs, large marine reptiles that lived during the late Cretaceous period, have been found in Mississippi. A team of geologists recently discovered a large vertebra in the east-central part of the state. The fossil is believed to belong to a mosasaur roughly 30 feet long, the largest ever found in Mississippi. Mosasaurs were apex predators with about 60 teeth and powerful tails. They lived in the Western Interior Seaway, a shallow body of water that split North America in two around 80 million years ago. They became extinct about 66 million years ago, when an asteroid impact caused a chain of events that collapsed the food chain on land and at sea.
Niagara Falls was temporarily shut off in the summer and fall of 1969. Engineers built a dam to divert water away from the American Falls so researchers could study the rock face, which was thought to be unstable due to erosion. The flow of water was halted for about six months. During that time, workers cleaned debris from the base of the falls, and tourists were able to walk on the dry riverbed. Millions of coins that had been thrown into the water over the years were removed. The falls have been diverted only once in this manner, though they stopped flowing naturally for about 40 hours in 1848 when ice blocked the source of the Niagara River.
Sightings of a large, unidentified aquatic creature in the Altamaha River in southeastern Georgia have been reported for centuries. The creature, sometimes called Altamaha-ha, has been described as a snake-like animal with a crocodile-like head and large teeth. The Muscogee Creek people told stories of such a creature long before European colonization. Reports continued into the modern era, with multiple sightings documented through the 20th century. No physical evidence of the creature has ever been found. In 2001, Scotland’s nature agency developed a contingency plan for the Loch Ness monster that would apply to any unknown aquatic animal: if captured, it would be sampled for DNA and released.
Several rivers around the world flow toward two different oceans. The Ikamesh River in Canada flows in both directions from a central point, running toward both the Hayes and Nelson Rivers. The Casiquiare in South America connects the Orinoco and Amazon river systems. The Partido stream in Argentina splits at a mountain saddle, with one branch reaching the Atlantic and the other the Pacific. North Two Ocean Creek in Wyoming divides into two branches, one reaching the Pacific and the other the Gulf of Mexico. Divide Creek on the border of British Columbia and Alberta splits at Kicking Horse Pass.
Lake Baikal in Siberia is the deepest and oldest freshwater lake in the world. It holds roughly one-fifth of the world’s liquid freshwater and is home to more than 2,500 animal species, about half of which exist nowhere else. The Baikal seal, or nerpa, is the only true freshwater seal in the world. It is believed to have traveled up rivers from the Arctic Ocean around 400,000 years ago. Since at least 1969, large rings have occasionally appeared in the lake’s winter ice. Research published in 2016 showed that the rings are caused by warm eddies circulating beneath the ice.
Several lakes around the world are notable for their unusual conditions. Lake Kaindy in Kazakhstan was formed after an earthquake in 1911 caused a landslide that flooded a valley, submerging a forest. The cold, clear water preserves the trees. Boiling Lake on the Caribbean island of Dominica has water temperatures between 180 and 197 degrees Fahrenheit near its edges. Lake Monoun in Cameroon is one of a few lakes that can experience limnic eruptions, in which dissolved gas suddenly erupts from deep water. Lake Natron in Tanzania has pH levels high enough to be corrosive, but it is home to more than two million flamingos. The Great Blue Hole off the coast of Belize contains a layer of hydrogen sulfide that prevents oxygen from reaching deeper waters.
In 1980, an oil rig drilling in Lake Peigneur in Louisiana penetrated the roof of a salt mine beneath the lake. The lake drained into the mine, creating a whirlpool that pulled in the rig, barges, a tugboat, and surrounding land. All 50 miners escaped, though the timeline of their evacuation was not fully detailed in the source. The lake, previously about 11 feet deep, was left with a new bottom at a depth of about 200 feet. The drilling company paid $45 million in damages. The accident was attributed to an engineer’s error in selecting drilling coordinates.
Lake Berryessa in California has a concrete spillway that resembles a giant drain. During the rainy season, water pours into the circular opening and travels through a tunnel into a nearby bay. The feature has become a popular attraction.
The Mariana Trench is the deepest known point in the ocean. It is home to organisms adapted to extreme pressure, including fish with transparent bodies and other deep-sea species. The Devil’s Kettle waterfall in Minnesota has a branch that disappears into a hole and was the subject of investigation after trackers and ping-pong balls failed to resurface. Researchers later determined that the water volume at the base of the falls matched the volume entering from upstream, suggesting the water reentered the river system, though the exact location has not been identified.
