1. The Boiling Lake, Dominica

If you’re heading to Dominica for a nice Caribbean retreat, don’t dip a toe in its boiling lake. It’s secluded on a high mountaintop in Morne Trois Pitons National Park, but that doesn’t make it a relaxing hot spring. This lake is literally boiling hot.

It sure looks like a giant witch’s cauldron, and cannonballing into this lake could result in death or at least serious burns. A thick cloud of steam surrounds it, warning tourists to stay out. Under this lake is the Earth’s molten hot mantle — with vents funnelling heat into the water from below.

2. Jacob’s Well, Texas

While many people want a relaxing vacation, others look for more thrills and action. So if you’re looking for places to go on daring dives, Jacob’s Well makes the top of the list as perhaps the most dangerous. It’s a deep, dark hole that descends into the unknown and tempts people wanting to escape the Texas heat.

However, this hole goes down 100 feet and becomes a dangerous cave labyrinth. It has incredibly narrow passages that can snag on divers’ equipment and endanger their lives. Multiple people have died swimming in this natural well, so don’t swim here.

3. Hanakapi’ai Beach, Hawaii

Hawaii is a vacation dream—beautiful beaches and warm weather abound—but even Hawaii has its dangerous beaches, which you should probably never swim in. At the forefront of that list is Hanakapi’ai Beach on the island of Kauai. First, it’s a fairly difficult (but gorgeous) two-mile hike to get to this beach.

Once you get there, the water often has dangerous rip currents, and several people have drowned in them. On top of all that, in the winter, this beach doesn’t have any sand anyway, so it’s not ideal for your typical beach-bum vacation. If you want to do the hike, skip getting in the water.

4. Bubbly Creek, Illinois

While you’re probably not going to Chicago to swim in its river, don’t jump into this section if inspiration makes you a little reckless on your trip. It has a long history of people dumping meatpacking waste into it, including blood, guts, and chemicals. The decomposition within it made the water bubble, giving it its cute name.

Once covered in black sludge so thick you could walk on it, Bubbly Creek is slowly recovering from its putrid past. Groups are working to make Bubbly Creek a happy ecosystem, but it still isn’t somewhere you should swim. Sometimes, sewer overflow is released into it, and on hot days, it still bubbles.

5. Samaesan Hole, Thailand

While Thailand has countless attractions to offer curious tourists and can be an amazing vacation destination, the Samaesan Hole is best left to the most experienced divers, if anyone at all. It’s about 280 feet deep and incredibly dark, in the middle of a busy shipping lane.

Strong currents and the depth and lack of visibility add to the dangers of this dive spot. However, if all of this still doesn’t deter you from wanting to swim here, this site is also an old military dumping ground. AquaWorld writes that there are still unexploded bombs underwater in the Samaesan Hole.

6. Lake Karachay, Russia

Russia may be an unconventional vacation spot, but it has plenty to offer tourists in the form of beautiful architecture and grand cities. It also has plenty of places you definitely don’t want to go, including the little Lake Karachay that no one should ever swim in.

During the 1950s, Lake Karachay was a dumping site for radioactive waste from the nearby Mayak processing plant. It got the glorious title of the most polluted place on the planet; it could kill someone within an hour. Think of it like The Simpsons’ Lake Springfield, so polluted that a dome was put over the fictional city. So, yeah, don’t swim here.

7. Eagle’s Nest Sinkhole, Florida

Florida can be a great vacation destination, between the warm beaches and opportunities to swim with manatees, but it has some less relaxing locations, like the Eagle’s Nest Sinkhole. At first, it looks like a normal pond, but it’s shaped like a sink: It has long, narrow passages underneath its basin.

Cave diving is already a dangerous hobby, but this deep dive takes it to a new level of life-threatening. Experienced divers have lost their lives in this dark underworld, so any casual tourist should never swim in the Eagle’s Nest Sinkhole. It even has a sign that says: “STOP: Prevent your death! Go no farther.”

8. Kipu Falls, Hawaii

Waterfalls are a peak hiking destination: They’re gorgeous and serene and represent the great beauty of nature. But not all waterfalls should be trifled with. For example, Kipu Falls in Hawaii has claimed several lives already. But you shouldn’t be going to this spot anyway since it’s on private property, and you’d be trespassing.

After guidebooks touted the spot as a “swimming hole extraordinaire,” visitors jumped off the top of the waterfall and into the pool below. This is where the spot gets dangerous — people struggle to swim safely once in the water. Generally, Kipu Falls is dangerous to people who have little experience in these sorts of environments.

9. ‘Maldives of Novosibirsk,’ Russia

Have you ever scrolled through Instagram and looked at all the pretty places you want to visit? Well, this popular Instagram spot should not be on your go-to list. While the water is a gorgeous turquoise reminiscent of the Bahamas, this lake is a power plant dump site in Siberia.

The water gets its color from calcium salts and metal oxides, while the coal ash pumped into it gives it a very high pH value. This can cause allergic reactions if people go in the water. So while this man-made lake isn’t nearly as dangerous as the previously mentioned dump site in Russia (Lake Karachay), don’t put it on your vacation dream list.

10. Lake Victoria, Africa

Situated between Uganda, Tanzania, and Kenya, Lake Victoria is massive. Millions of people live along its coasts and use its resources to make a living. However, about 5,000 people die each year on the lake, making it the most dangerous water on Earth, based on fatalities per square kilometre.

The biggest threat to Lake Victoria is its volatile weather, which whips small vessels around easily. Many of the fishermen working on the lake don’t have life jackets, which is a recipe for disaster. However, a new text message-based weather alert system is helping to save people from the danger.

11. Horseshoe Lake, California

If you’re heading off to Mammoth Lakes or Mammoth Mountain in California, you should steer clear of this little mountain lake. About 30 years ago, earthquakes caused magma to rise under the mountain. After that, cooling magma caused carbon dioxide into the soil around Horseshoe Lake.

Carbon dioxide gas has killed many trees around the lake by starving their roots of oxygen. While the gas in the area seems to be decreasing, it can collect in poorly ventilated places like snowbanks, depressions, and tents, posing a deadly threat to people.

12. Rio Tinto, Spain

This Spanish river is an attraction for history nuts, not river rafters. Its mineral content (including copper, gold, silver, and iron) garnered it enough attention in ancient times that it has become known as the birthplace of the Copper Age and Bronze Age.

Since the Red River was excavated and mined extensively, it has become very acidic and thus isn’t a good swimming spot. However, if you’re into science, it has interesting extremophile bacteria living in it and is possibly similar to an underground acidic ocean on Europa, Jupiter’s moon. So, visit Rio Tinto if you’re into science and history, but don’t go in the water.

13. The Ganges River, India

While plenty of people swim in the Ganges River every summer, some experts advise that they shouldn’t. The river is incredibly polluted with sewage, industrial waste, and even corpses. But that doesn’t stop kids from taking swimming lessons in it.

The Ganges is a goddess in the Hindu faith that purifies water, so people are reluctant to stop swimming in it. However, untreated sewage is dumped into it each day. Part of the river (in the Himalayas) is crystal clear, but it becomes polluted and disease-ridden when it snakes through cities. On top of that, the part of the river that doesn’t have dangerous currents is the most polluted.

14. Shark Alley, South Africa

South Africa is a great scuba diving and whale-watching spot if you’re into that kind of vacation. In fact, the town of Gansbaai calls itself the “Great White Shark Capital of the World” because Shark Alley—a channel teeming with great whites—is just off its coast. 

It’s a popular spot for cage diving (when you get in a large cage underwater with chum, or bait, around you to tempt sharks into swimming by). However, while you can go cage diving in Shark Alley, you cannot swim freely in these waters without a special permit (despite what the movie Dark Tide shows).

15. Hoover Dam, Nevada

Sure, people visit the Hoover Dam to marvel at its engineering, but no one’s going there for a swim. It’s illegal to swim near it because it is so incredibly dangerous due to the 10 turbines underwater, which can suck a person to their death.

One guy successfully swam across it but only survived because nine of the turbines were off. When he came ashore, he was fined $330 (he’d also been partying for 37 hours straight leading up to this swim). So while this one person survived, swimming in the Hoover Dam spillways may be your last time.

16. Citarum River, Indonesia

Like the Ganges River, the Citarum River in Indonesia is heavily polluted and has even been called the “world’s dirtiest” river. It’s been crucial to the people living on and around it in major cities like Jakarta, but industrialization has changed it drastically.

Textile factories along its bank dumped toxic waste into the water, and people living along it used it as a trash dump, even though it was also their source of water. There simply wasn’t a proper waste management system in the area to accommodate all the new residents flocking to the factories.

17. Blue Lagoon, England

This spot was once a quarry where materials were extracted for industrial use. Still, the calcium oxide left in it has given the water a very high pH (comparable to ammonia’s). On top of that, people dump vehicle parts and other trash. But that pretty blue colour has lured in plenty of swimmers.

The water can cause skin irritations and stomach problems, but it’s too dangerous for the water supply to drain. So, to discourage people from going in the water, the town dyed it black. Now, it doesn’t look like a little Bahamas paradise anymore.

18. Some South Carolina beaches, South Carolina

Generally, South Carolina beaches are safe for swimming. However, they still have some dangers. For example, rattlesnakes have been randomly showing up on the beaches: Some are coming out of the water, some are going in for a swim, and some are just chilling in the nearby grasses.

South Carolina has six species of venomous snakes, with many snakes on the coastal islands. Generally, they prefer land, but sometimes they wind up in swamps, on beaches, or in the ocean. On top of that, Myrtle Beach’s water can be filled with bacteria the day after a particularly heavy rain.

19. Réunion Island, Indian Ocean

While shark attacks are generally very rare (in fact, humans kill millions more sharks than sharks kill humans), this island off the coast of Madagascar has a bit of a reputation for them. In fact, surfing is banned in sections of the surrounding waters due to bull sharks.

Earlier this year, a man was surfing in a restricted area when he was attacked and killed by a shark. That became the 11th fatal (reported) shark attack on the island since 2011. While some areas around the island may be safe for surfing, check with the local government for safety’s sake before swimming in these waters.

20. Bolton, Strid, England

What appears to be a small, charming creek in England is just a slim section of the larger River Wharfe. The current in the Bolton Strid is powerful and dangerous and can claim lives if one is to step into it. Legend has it that no one who’s entered the water has ever come alive.

Signs line the banks, telling people to stay back and not go in the water. Two writers in the 1800s even wrote about the Strid in the poem “The Force of Prayer” and the short story “The Striding Place.” This little “creek” has quite a reputation.

21. Northern Australia, Australia

While Australia’s beaches are a huge draw to tourists, some of the beaches on the northern side of the continent can be quite dangerous between the months of November and May. (Of course, there are always dangers since it’s Australia.)

But this is when and where venomous box jellyfish are most abundant. In fact, some beaches are completely closed during this season. Whenever going for a swim in Australia (or anywhere, really), always pay attention to beach signage. These places are closed for a reason. If you’re stung in Australia, dial 000 for emergency help.

22. The Devil’s Pool, Zambia

If you’re an adrenaline junkie, you can go on a guided tour of this pool at the top of a 328-foot drop, but if you’re more of an anxious person, skip this trip. Either way, you shouldn’t swim in The Devil’s Pool atop Victoria Falls without highly experienced, trained guides.

At the top and edge of the world’s largest waterfall is a slim rock that can keep swimmers from plummeting to their death (but only during the dry season, mid-August to mid-January). Any other time of the year, this place becomes a death trap in which to swim.

23. Potomac River, United States

A stretch of the Potomac River between Great Falls and Chain Bridge has proven itself to be quite deadly, so hikers beware. Even grabbing a ball from the shallows of this area, known as Mather Gorge, can be life-threatening. Kayaking can be dangerous here, too.

The problem is that a powerful current surge below while the river may appear calm on the surface. There are signs that say “No Swimming,” but some people disregard these, don’t see them, accidentally slip, or think a step into the shallows won’t hurt. Several people die here each year, so just don’t go into the water (which is also illegal).

24. Lake Kivu, Africa

Lake Kivu is a complicated place. It’s situated between conflicted Rwanda and the Democratic Republic of the Congo, has a buttload of gas inside waiting to explode, and could provide electricity to the poor communities on its shores. While it can be fine to swim here, this lake isn’t the safest in the world.

Carbon dioxide and methane lie within, sometimes seeping out and suffocating people on its banks or waters. Children frequently drown in the lake when getting buckets of water. Plus, it may have dangerous bacteria inside that can make swimmers sick. People have been working on the gas problem, however, because if they don’t, the lake could explode.

25. The Blue Hole, Egypt

If you’ve learned anything from this article, it’s probably that diving into sinkholes and underwater caves is very dangerous. The 394-foot-deep Blue Hole of Dahab, Egypt, is no different: It’s dark, deep, and a challenge enticing to daring divers.

At depths past about 100 feet, nitrogen narcosis may begin to affect your body, inducing a sort of drunken state. This can include impaired judgment, overconfidence, euphoria, and confusion, which can cause further problems, especially in an underwater cave. An estimated 130 people have died from diving into The Blue Hole in the last 15 or so years.

26. Bangkok’s Canals, Thailand

While Bangkok is sometimes called the “Venice of the East,” you should probably not swim in any of the canals snaking through the city. They are polluted, similar to the previously mentioned Ganges and Citarum Rivers.

People frequently use boats on these canals to get around the city, but they don’t make for great swimming waters. These canals have been very important to Bangkok, serving as important transportation, but some have been filled in with cement and turned into roads. These can be a good history and culture stop on a vacation, but leave the swimming for elsewhere.

27. Laguna Caliente, Costa Rica

This toxic lake is literally on a volcano and probably one of Earth’s harshest environments. The water is so hot it could burn you and is incredibly acidic (like, 10 million times more than tap water). It’s kind of similar to hot springs that used to be on Mars.

While you should never go swimming in this lake, one organism lives in it: a bacterial species. Scientists are studying this lake and its inhabitants to try and better understand Mars. On top of the near-boiling water temperature, sulfuric acid fumes are around the lake.

28. Lake in Kawah Ijen volcano, Indonesia

It should probably be a rule that if you find a lake on a volcano, don’t swim in it. On the Kawah Ijen volcano, magma is the world’s largest acidic lake. Its turquoise colour comes from various dissolved materials, like hydrochloric acid and sulfuric acid. Magma is trying to get free under the lake and its volcano.

A gas plume rises from the crater, possibly made of gases the magma releases. The plume may be largely made of steam, with the addition of carbon dioxide, sulfur dioxide, and other toxic gases. So unless you want to turn into the Joker, you probably shouldn’t go for a swim in this volcanic lake.

29. Berkeley Pit, Montana

This super-creepy pit was once an open-air copper mine but is now filled with acidic water and toxic waste. It’s huge! Within its reddish water is an alphabet soup of heavy metals and toxic chemicals, including iron, copper, zinc, arsenic, and sulfuric acid.

If you drink enough of this water, it will corrode your digestive system and kill you. So it can’t be good to swim in it. However, some fungi and bacteria do live in this nasty water. They’ve adapted to their harsh environment, and scientists have even looked into them for ways to help fight cancer cells.

30. The Nile River, Africa

While sharks may scare tourists from oceans and beaches, the Nile’s crocodiles should scare you more. Crocodiles are one of the deadliest animals on Earth, killing perhaps 1,000 people per year (compared to sharks’ 10 or fewer). They hold the title of deadliest large African animal.

If you’re from Florida and think you’re used to huge reptiles, think again. Nile crocodiles are far more aggressive than their American counterparts. On top of these very large threats, there’s the much smaller threat of disease. For example, you can get schistosomiasis, which occurs in the Nile River Valley, from contaminated freshwater.