Almost three-quarters of our blue planet is covered in water, and for an equally accurate and verifiable statistic absolutely every inch of it is terrifying and evil. Much of Earth’s water is unexplored, deep, dark, frigid, and home to nightmare-inducing creatures that float through the seas like slimy ghosts. Even the shallows we’re familiar with can come with treacherous rapids, hidden caves, boiling vents, noxious gas plumes, and more. Somehow, despite all of that, diving remains a super popular pastime.
Every year, millions of divers suit up and sink down into pretty much any body of water that they can. In the process, many remerge with transcendent memories and breathtaking photographs, but also: many die. About 100-200 of them each year, on average.
This list contains both spots known to have taken divers and those with untapped lethal potential, but all of them are some of the deadliest places to scuba dive.
# Battery Acid BathTechnically, this entry is more thousands of places than one, but they all share one deadly property: acid water. For some of these caustic bodies, their water is more acidic and more concentrated than even battery acid.
Bodies of water can become overly acidic in several ways, but one standard method is through drainage from a nearby mine. Coal mines tend to be the worst offenders, inadvertently (and sometimes purposefully) dumping acidic metals and sulfides into rivers and lakes. Oddly enough, the result is occasionally beautiful, turning rivers deep red, orange, yellow, or green. Diving in these waters, though, is a death sentence; the water in one mine in Iron Mountain in California was found to be the most acidic ever discovered. Its pH: -0.7!
It’s likely you just learned that the pH scale can go below zero, and that should tell you how dangerous these waters can be.
# Lake NyosWhen a body of water kills so many people, so quickly, that it becomes the namesake for a famous disaster, you can bet that steering clear of its water is a good idea. In 1986, Lake Nyos in northwestern Cameroon did just that when the “Lake Nyos Disaster” killed more than 1,700 people.
Essentially, Nyos’s waters have the misfortune of resting above pockets of underground magma, which constantly leak CO2 upwards. The result is that the lake is prone to a rare phenomenon known as a limnic eruption, which causes huge amounts of CO2 absorbed into the water to suddenly erupt from the water as a cloud of toxic gas. This cloud, some 100,000-300,000 tons of CO2, shot out of the Lake’s waters, spread throughout the immediate area, including several local villages and 1,746 people.
# The Boiling LakeThe lake’s name says it all on this one. Hidden within the lush, tropical mountains of the Caribbean island of Dominica lies Boiling Lake, and that title is hardly metaphorical. Essentially, it’s a flooded fumarole.
Though it’s hard to find any recent records of the water’s temperatures, as presumably, scientists are more rational these days, a record from two scientists in 1875 put the temperature at the water’s edge at 180 to 197 degrees Fahrenheit. However, they could not record temperatures farther in the lake, as the water was literally boiling, damaging both their instruments and their bravery.
# Iceberg B-15Moving from one temperature extreme to another, we have Iceberg B-15, which you may have heard of. At over 3,200 square miles, it was the most enormous iceberg ever recorded until enough chunks broke off to give another the crown. B-15 contained caves and water, and therefore, of course, people cave dove in it.
Three filmmakers for National Geographic decided to dive into the icy, black waters inside the iceberg’s caves, and their account of the trip is harrowing. Some tidbits, as terrifying as they are tantalizing, from diver Jill Heinerth are as follows: “One minute is dangerous. I mean you very, very quickly lose the ability to manipulate your hands or operate or even think straight,” “There were also strange cracks and pops and groans from the ice. It was moving, it was shifting, it was changing,” and “The cave tried to keep us today.”
# The Blue HoleIf you’re familiar with scuba diving, or even just the bevy of “Most Extreme” specials that Nat Geo airs on a loop, then you’re likely not surprised that the Red Sea’s blue hole makes the top spot on this list. If you are surprised, it’s likely that you don’t know the site by either of its nicknames: “World’s Most Dangerous Dive Site” and “Divers’ Cemetery.”
There are blue holes, substantial marine sinkholes where otherwise clear waters quickly fall into crushing depths and darkness, all over the world. Many have gained notorious reputations from divers, but none more so than the blue hole off the coast of Dahab, Egypt. Its actual body count is unknown but is estimated to be around 200.
Though its challenges are straightforward, they are nonetheless tricky enough to be deadly. According to diving instructor Alex Heyes, divers attempting to swim under the hole’s rocky arches are often unaware that “this challenge is to scuba divers what Kilimanjaro is to hikers.” And as such, the fatalities continue.