10 Places You Don't Want to Swim


These 10 lakes, pools, and beaches should be approached with caution—or not approached at all.

1. Laguna Caliente

Volcanoes do crazy things to water. With a pH as low as "slightly below zero," Laguna Caliente (situated in the summit crater of Poás Volcano) is probably the most acidic body of water on the planet. The rain that falls around the area has a pH of 2.0 on average.

2. Nyriragongo Crater's lava lake

Two hundred and eighty-two million cubic feet of molten rock won't make for a pleasant game of Marco Polo, but you can probably roast a marshmallow from several hundred yards. The world's largest permanent lava lake rests in one of the eight volcanoes of the Virunga range of Africa. Last year, a team of scientists and explorers survived a journey to the rim of the lake, which is detailed here in a stunning photo essay.

3. Just about any body of water in China

Heavy traffic (both on roads and waterways), industrial pollution, and uncontrolled fertilizer use have contributed to a national water crisis in China. Nearly every major lake and river in the country is currently experiencing toxic green-blue algae bloom. Greenpeace tested waters in 25 regions and found 20 of the samples too high in nitrogen and nitrates to be safe for human use. In fact, the concentrations were so high that the water can't even be used for watering plants or industrial purposes.

4. Lake Karachay

In Soviet Russia, lake contaminate you. From 1951 until 1968, this small lake in the Ural Mountains was used as a toxic dump site for Mayak, a nuclear waste storage and processing facility. Between 1978 and 1986, the lake was filled with concrete blocks to prevent the shifting of irradiated sediment. In 1990, the radiation level measured more than high enough to deliver a lethal dose to a human within an hour.

5. Any exploding lake

There are only three known exploding lakes in the world: Lake Kivu in Rwanda and Lakes Monoun and Nyos in Cameroon. Created by a dam of volcanic rock, this type of lake lies atop a pool of magma that releases carbon dioxide and methane into the water. On occasion, a large pocket of toxic gas will "explode" from the water (a limnic eruption); this happened in 1984 at Lake Monoun, killing 37 people, and again in 1986 at Lake Nyos, suffocating 1700 people and 3500 livestock.

6. Berkeley Pit

Formerly an open-pit copper mine, the Berkeley Pit in Butte, Montana, is filled with acidic, highly oxygenated water that leaches heavy metals from the surrounding rock. The Superfund list of contaminants is arsenic, cadmium, copper, zinc, and lead. In 1995, a flock of 342 geese was found dead in the Pit with burns from the water in their internal organs.

7. Lake Vostok

Lake Vostok is an oligotropic subglacial lake under the Antarctic. Information collected from ice cores will reveal whether life has survived in isolation for 15 to 24 million years and the probability of life in subsurface water on other planets. Even if scientists discover ice-loving fish below, you can't swim there—the average water temperature is calculated to be -3ºC.

8. Boiling Lake in Dominica

Featured in the Angry Planet episode, "Across the Boiling Lake," the flooded fumarole's shore temperature is between 185 and 197ºF, but the central area of the lake hasn't been measured because no one can get there safely. It can be clearly observed that the water is actively boiling, however, so showing off your sweet cannonball skills is probably a bad idea.

9. The Amazon Basin

Even Hank Hill's narrow urethra wouldn't save him from the candiru (or toothpick fish) native to Amazonian waters. Though formal experimentation shows the fish is not attracted to urine (as previously believed), it is in fact small enough to, uh, invade a person. One such incident was documented in 1997; the "River Monsters" episode of Animal Planet investigated the claim, which was fully verified.

10. The Northern and Eastern beaches of Australia

Remember the scene in Finding Nemo when Marlin and Dory are in the jellyfish field? That's a slightly exaggerated idea of what the coastal waters of Australia are like, except these are lethal box jellyfish (and blue-ringed octopus, cone shells, scorpion fish, crocodiles, and sting rays) and you're not an animated fish.

Take Advantage of Amazon's Early Black Friday Deals on Tech, Kitchen Appliances, and More


This article contains affiliate links to products selected by our editors. Mental Floss may receive a commission for purchases made through these links.

Even though Black Friday is still a few days away, Amazon is offering early deals on kitchen appliances, tech, video games, and plenty more. We will keep updating this page as sales come in, but for now, here are the best Amazon Black Friday sales to check out.


Instant Pot/Amazon

- Instant Pot Duo Plus 9-in-115 Quart Electric Pressure Cooker; $90 (save $40) 

- Le Creuset Enameled Cast Iron Signature Sauteuse 3.5 Quarts; $180 (save $120)

- KitchenAid KSMSFTA Sifter with Scale Attachment; $95 (save $75) 

- Keurig K-Mini Coffee Maker; $60 (save $20)

- Cuisinart Bread Maker; $88 (save $97)

Home Appliances


- iRobot Roomba 675 Robot Vacuum with Wi-Fi Connectivity; $179 (save $101)

- Fairywill Electric Toothbrush with Four Brush Heads; $19 (save $9)

- ASAKUKI 500ml Premium Essential Oil Diffuser; $22 (save $4)

- Facebook Portal Smart Video Calling 10 inch Touch Screen Display with Alexa; $129 (save $50)

- Bissell air320 Smart Air Purifier with HEPA and Carbon Filters; $280 (save $50)

Video games


- Legend of Zelda Link's Awakening for Nintendo Switch; $40 (save $20)

- Marvel's Spider-Man: Game of The Year Edition for PlayStation 4; $20 (save $20)

- Marvel's Avengers; $27 (save $33)

- Minecraft Dungeons Hero Edition for Nintendo Switch; $20 (save $10)

- The Last of Us Part II for PlayStation 4; $30 (save $30)

- LEGO Harry Potter: Collection; $15 (save $15)

- Ghost of Tsushima; $40 (save $20)

Computers and tablets


- Apple MacBook Air 13 inches with 256 GB; $899 (save $100)

- New Apple MacBook Pro 16 inches with 512 GB; $2149 (save $250) 

- Samsung Chromebook 4 Chrome OS 11.6 inches with 32 GB; $210 (save $20) 

- Microsoft Surface Laptop 3 with 13.5 inch Touch-Screen; $1200 (save $400)

- Lenovo ThinkPad T490 Laptop; $889 (save $111)

- Amazon Fire HD 10 Tablet (64GB); $120 (save $70)

Tech, gadgets, and TVs


- Apple Watch Series 3 with GPS; $179 (save $20) 

- SAMSUNG 75-inch Class Crystal 4K Smart TV; $998 (save $200)

- Apple AirPods Pro; $199 (save $50)

- Nixplay 2K Smart Digital Picture Frame 9.7 Inch Silver; $238 (save $92)

- All-New Amazon Echo Dot with Clock and Alexa(4th Gen); $39 (save $21)

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14 Unique Christmas Gifts on Uncommon Goods

Uncommon Goods
Uncommon Goods

This article contains affiliate links to products selected by our editors. Mental Floss may receive a commission for purchases made through these links.

Sometimes it’s hard to find just the right gift for someone you care about. If you want to avoid getting a loved one the same ol' pair of winter socks or gift cards like last year, we found 14 unique gifts on Uncommon Goods that are perfectly suited for a range of different tastes and interests.

1. Personalized Hand-Written Letter Blanket; $160

Uncommon Goods

Bring warmth into someone's life—in more ways than one. This 100 percent cotton throw blanket is made to resemble a heartfelt letter written on notebook paper. Your sentiments (limited to 400 characters or fewer) will keep your friend or family member cozy all year long.

Buy it: Uncommon Goods

2. Personalized Puzzles Book; $40

Uncommon Goods

This gift is perfect for the person who’s hooked on Sudoku puzzles and fills out the daily crossword in pen. Inside, you’ll find more than 50 pages of crosswords, word searches, and Sudoku puzzles. One page of puzzles is devoted to trivia on a year of your choice, letting you honor the gift recipient’s birth year, anniversary, or graduation, to name just a few ideas. Plus, there’s space inside to include a personalized dedication.

Buy it: Uncommon Goods

3. Custom Travel Photo Coasters; $65-$75

Uncommon Goods

With this customizable gift, you can turn precious memories into a classy set of marble coasters that resemble antique Polaroids. A set of four custom coasters with photos alone comes in at $65, but you can choose to add unique captions for an extra $10.

Buy it: Uncommon Goods

4. Custom Pet Pillow; $145

Uncommon Goods

Turn your loved one’s beloved pet into an adorable pillow. Reviewers say that it’s high-quality and surprisingly lifelike—you may not be able to tell the pillow apart from your pet at first glance.

Buy it: Uncommon Goods

5. Personalized Moonshine Jug & Kit; $50

Uncommon Goods

This personalized moonshine jug also comes with flavorings you can use to make your own custom hooch. Simply pour some grain alcohol or vodka into the jug, add a little of the included apple pie, peach, or cherry flavoring, and you’re all set with some “bootleg” booze of your very own.

Buy it: Uncommon Goods

6. Family Pebble Portrait; $110

Uncommon Goods

New York artist Wendy Pound uses found pebbles, seashells, flowers, and driftwood to create beautifully unique family portraits. You can even choose to feature your family cat or dog.

Buy it: Uncommon Goods

7. Custom Message Shortbread Cookies; $38

Uncommon Goods

For some people, the best gifts come in delicious, sugar-filled packages. For $38, send a customized box of 24 cookies to your favorite sweet-toothed friend. Each cookie can accommodate up to three lines of text, with a maximum of 12 characters on each line.

Buy it: Uncommon Goods

8. Personalized M Is for Me Book; $40

Uncommon Goods

Young children will get a kick out of reading their own names in this personalized picture book that describes positive traits for each letter of the alphabet. In addition to customizing the title, you can also choose the cover color and add a short dedication to the recipient.

Buy it: Uncommon Goods

9. Periodic Table of Flavor Rub Set; $60

Uncommon Goods

Spiceology has taken the beloved periodic table and turned it on its head by converting elements into unique spice rubs like Ch for Chile Margarita, Oh for Oh Canada, and Ec for Cowboy Crust. This is the perfect gift for friends that like to try new flavors or science fans that love the play on elements.

Buy it: Uncommon Goods

10. Frank Lloyd Wright Double Sided Puzzle; $16

Uncommon Goods

Architecture buffs out there know Frank Lloyd Wright broke the mold when it came to his building designs. This puzzle is also breaking the rules by making double-sided puzzles featuring some of the architect’s most famous creations. These 500-piece puzzles showcase either the Solomon R. Guggenheim Museum or Fallingwater on the front, with the buildings' respective floor plans on the back.

Buy it: Uncommon Goods

11. Great Women of Science Pint Glass; $18

Uncommon Goods

Even though their work has often been overshadowed by their male counterparts, women have been making huge strides in science for centuries. And Cognitive Surplus wants to celebrate these figures in the form of pint glasses showcasing portraits of scientists like Rosalind Franklin, Marie Curie, and Elizabeth Blackwell.

Buy it: Uncommon Goods

12. 100 Movies Scratch-Off Poster; $15

Uncommon Goods

If you know a film buff with a bit of an obsessive bent, this scratch-off poster could be their perfect outlet. The poster itself features tiny square images of 100 classic movies, from Charlie Chaplin to Pixar, but upon arrival, all the pictures will be grayed out. It’s your loved one’s job to scratch off the foil covering as they complete more and more of the movies highlighted on the poster.

Buy it: Uncommon Goods

13. Democracy Coasters; $50

Uncommon Goods

Sections of some of the United States’s most cherished historical documents are beautifully reprinted onto these marble coasters, including the Declaration of Independence, the Constitution, the Bill of Rights, and the Civil Rights Act.

Buy it: Uncommon Goods

14. National Parks Notebooks; $13

Uncommon Goods

These notebooks tout a vintage travel poster vibe, and best of all, they’re all inspired by some of the most beautiful National Parks the United States has to offer. They’re available in packs of three, each with a different batch of covers. This way, you can tailor your choice to your loved one’s favorite spots.

Buy it: Uncommon Goods

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