Summer is just starting and I’ve already found myself, multiple times, in natural bodies of fresh water that descended far deeper depths than I was prepared for. On one occasion, believing the riverbed to be no more than a few inches below my toes, I propelled myself down into the dark waters, stretching for the muddy bottom only to find it nowhere in reach, my lungs screaming for air. But need or air was not the only thing forcing me to the surface. The moment the riverbed was not right where I expected it, a familiar image came to my mind: that of a sea monster rapidly closing the distance between its sharp, protruding teeth and my fleshy toes. As I frantically kicked my way to the rocky shore, a slideshow of underwater monsters played in my mind, starting with the deep-lake horror movie The Quest (okay, it’s not really a horror film, but to my too-young-to-watch mind, it was terrifying), followed by 20,000 Leagues Under the Sea, Jaws, Deep Blue Sea, Anaconda, and the list goes on….

That day, forcing myself back into the water, I realized sea monsters really are the worst, as in the best, monsters. First, they are one of the few monster archetypes that are actually kind of real. To us, the kraken is an iconic mythic sea monster, but for 12th century Norwegians, it was a very real threat. No, what they saw, or rather what they said they saw (better to err on the side of exaggeration, right?), did not stretch over a mile in length, or have six heads, or devour an entire ship.

But, many of the early descriptions are consistent with what we now know as the giant squid, or, depending on the location, the giant octopus, or the MASSIVE lion’s mane jellyfish with tentacles alone that stretch 120 feet. This sea monster is found mostly in the North Pacific, can expand to nine feet in diameter, and has a poisonous sting. And the best part: not only does it like to float close to the surface, they sometimes form a swarm. Imagine what it must have been like for early sailors, venturing into the never-ending ocean and seeing these huge creatures for the first time (it’s no wonder Europeans believed unicorns were real—a horse with a horn seems far more believable than, say, the sloth or platypus). It shouldn’t be surprising, then, that many of the sea creatures have been aptly given monster names: the vampire squid, the horrible goblin shark. (if you love monsters, check out Pliny the Elder’s Natural History, a complete catalog of all animals known and imagined from 77 A.D.).

Next, everything is more scary in the water. Godzilla is scary. Godzilla coming at you from 23,000 feet under the sea is terrifying.

You’ve seen it a hundred times: a figure, alone in the open water, no land in site, physical exhaustion setting in, unknown predators circling just below the surface, total silence except for the sound of a distant splash.

This scene incites a sense of anxiety and real panic for a number of reasons, namely our most effective tools to deal with threat and uncertainty are rendered useless in the water. This is why some report a strong sense of claustrophobia when swimming. While getting caught in open water (or just thinking about it), doesn’t fit with the clinical definition of claustrophobia that focuses on anxiety around tight spaces, the fear of suffocation by drowning and not being able to escape can replicate the feeling of getting stuck in an elevator. At the core is the loss of control and a feeling of helplessness.

Our sight is not helpful: unless we’re in the blue lagoon, we can’t see much below the surface, or farther than a few feet in front of us. Our hearing isn’t doing much for us, no stomping or growling to give the monster’s approach away, no breaking twigs, rattling door handles, or breaking windows. Try watching Jaws again focusing on sound, the “duh-dun” is made all the more impactful because of the silence in the rest of the film. And while we can swim pretty well, we’re not all Michael Phelps (who is apparently racing a shark), and our bodies evolved to excel on land, not water. Yes, humans are incredibly adaptive, or rather, we’re really good at adapting our environments to our needs. How many other animals can survive on the equator or in the arctic? Oxygen tanks may provide a workaround, but there is no working around the reality that we would quickly perish were a sea monster to wrap its tentacles around our ankle and drag us into the abyss.

Try to hold your breath right now and see how long you can last. Most of us last less than a minute before we start to panic. Part of that is because we’re not as efficient at taking in oxygen as marine mammals. Dolphins, for example, exchange around 80% of air when they breathe, compared to our 17% (although we don’t have to think about breathing like they do—can you imagine having to stop every 30 seconds and remind yourself to breathe?). It’s not just about oxygen, carbon dioxide can build up, basically suffocating us from the inside out. We’re also not well-suited for deep, or quick, dives. For comparison, professional freediver Aleix Segura Vendrell, from Spain, held his breath for a record-breaking 24 minutes and 3 seconds in a motionless float, while the record while diving is 3 minutes and 38 seconds, set by Nicholas Mevoli, who tragically lost consciousness and died shortly after surfacing. Yeah, terrifying.

The deep sea, and really all deep waters, are still such a mystery, and fear is all about the unknown, the inability to predict what is out there, where it might be, and what it could do to us. (Don’t look at this guy’s Twitter feed if you don’t want nightmares.) All of this to say go out and have a great summer of fun in deep waters! Get comfortable with the uncertainty and pay no attention to the creatures lurking in the dark. Unless you’re trying to scare your friends, or get them OUT of the water fast. In that case, tell them this creature, aptly named the yeti crab, discovered in 2005 and looking straight out of the mind of Guillermo del Toro, is coming to snap off their toes:

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