Top 20 Most Dangerous Ocean Creatures in the World

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Top 20 Most Dangerous Ocean Creatures in the World

WRITTEN BY: Sean Frankling
Who's up for a swim? For this list, we'll be looking at the meanest, nastiest, and most dangerous denizens of the deep. Our countdown includes Stonefish, Sea Lion, Great White Shark, Bull Shark, Sea Snake, and more!
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top 20 deadliest ocean creatures


Welcome to WatchMojo, and today we’re counting down our picks for the top 20 deadliest ocean creatures.

For this list, we’ll be looking at the meanest, nastiest, and most dangerous denizens of the deep. We’ll look at their most worrisome features as well as how many lives they’ve taken. We won’t be including things like the pufferfish, which are only deadly when eaten.

What horrors do you worry about down in the murky blue? Let us know what nightmare fish keep you up at night in the comments.

#20: Portuguese Man o’ War

The Portuguese man o’ war may look like the mostly deflated straggler from a bunch of balloons, but it stings like a swarm of bees. Normally, they float along the ocean surface, paralyzing any fish that happen to wander too close to their tentacles and dragging them into their mouths. Lucky for you, humans are usually too big to get tangled up and paralyzed. But that doesn’t mean getting stung won’t hurt. A lot. Stings from a Man o’ War’s tentacles can leave long red welts. And in extreme cases, they can cause something like an allergic reaction that can close up your throat or send you into shock. All but the most severe stings are survivable, but they definitely don’t sound fun.

#19: Stonefish

You thought stepping on Lego was bad. This small breed of fish has an unusual look: it resembles a rock bed, which is very useful for warding off predators. Unfortunately, those who accidentally tread upon the stonefish will be greeted with sharp fins that can pierce through shoes. On top of the initial painful sting, victims also have to contend with a neurotoxin that can shut down their respiratory system and even cause their heart to fail. Yikes. Found in the Indo-Pacific area, the stonefish is a delicacy in some places – after cooking has destroyed the venom, that is.

#18: Flower Urchin

Unlike the other toxic hacky sack-like creatures in their family, flower urchins look less pointy and more squishy than their relatives. But they’re not. They’re covered with spines and little round feelers on stalks that look just like, you guessed it, a bouquet of flowers. But do not smell them. When those little blooms sense a threat, they clamp shut and inject an incredibly painful toxin. They can even break off little pieces of themselves - which are basically the claws of what’s known as the pedicellariae - to get stuck in your skin and keep pumping it into you for hours. There have been alleged reports of urchin encounters having fatal consequences. But fortunately, no cases have been definitely confirmed.

#17: Shortfin Mako Shark

This is not a face you’d want to kiss. Not if you want to keep your lips in one piece, anyway. Mako sharks are known for their jagged grins and their unbelievable speed. Reaching speeds of over 60mph, they’re basically living torpedoes. You’d think that would make them pretty dangerous, and you’d be right. Although, let’s be honest, just about anything faster than a flounder can outswim most humans. Shortfin Makos have only been responsible for one confirmed fatality out of a total of 9 reported attacks. This suggests they’re probably not that interested in taking down humans. In fact, many of those injuries historically happen when sport fishermen go after them. So it's pretty hard to blame the sharks.

#16: Blue-Ringed Octopus

Such a pleasant name for such a debilitating beast. In regards to killing power, the blue-ringed octopus’ claim to fame is its infusion of the neurotoxin TTX, or tetrodotoxin, into its bites. Humans in particular face the risk of TTX shutting down their respiratory system, which can mean death for those without immediate medical attention. Considering that one blue-ringed octopus contains enough TTX to kill up to 26 humans – within minutes - and that TTX is thousands of times more potent than cyanide, the threat here is potent.

#15: Orca [aka Killer Whale]

Let’s get one thing straight: there has only ever been one documented instance of a human being bitten by a wild Orca and no recorded fatalities. That being said, they’re bigger than great white sharks, highly intelligent, and known to employ pack hunting tactics on prey, ranging from seals to larger whales. For sheer size, strength, and smarts, Orcas rate among the most effective predators in history. They’re even known to team up to use waves as ranged weapons to knock prey off of ice floes, which pretty much sounds like one step removed from an actual comic book superpower. We can tell Orcas aren’t interested in eating us because if they were, none of us would ever get back out of the ocean.

#14: Sea Lion

Some species of sea lion can weigh anywhere from 600 pounds to a full ton. The good news for humans is that sea lions mostly eat fish, so you’re probably not on the menu. But that doesn’t mean you can relax just yet. Sea lions can also get fiercely territorial. On rare occasions, that has resulted in them biting humans and even yanking them into the water. While that definitely sounds like a terrifying experience, sea lions are like orcas in that they don’t seem that interested in attacking us. If they were, those huge teeth and a top swimming speed of 25 mph would mean we’d hardly stand a chance.

#13: Leopard Seal

Leopard seals have been aggressive to humans on several notable occasions. Normally, they eat krill, other seals, and the odd penguin. But there are several records of them chasing Antarctic explorers across the ice or even dragging them underwater. In 2003, one managed to drag down a snorkelling biologist, who sadly did not survive. Luckily for most of us, leopard seals live in the waters off the coast of Antarctica. So unless you’re one of the few people who travel there for research, you’re never likely to run across one. Still, if you ever visit, be sure to stay away from the edges of the ice. They like to shoot up out of the water and surprise their prey there.

#12: Moray Eel

Found most often in oceanic or brackish water, moray eels typically avoid contact with humans whenever possible. When sufficiently threatened, though, these creatures ensure their aggressors get what’s coming to them – and more. Moray eel bites can produce easily-infected wounds, on account of the eels having a large amount of bacteria in their mouths. And that's not getting into their ability to chase down and kill other fish with minimal effort – small sharks have even fallen victim to their attacks. Who ever said the electric eel was the only threatening eel around?

#11: Great Barracuda

Fast, vicious, and capable of incredible injury – that's a frightening combination. With some recorded as growing almost as long as 7 feet, giant barracuda are also known for being quick swimmers... and for being keen on brutal ambushes. They lie in wait before charging forth and biting down on their prey, armed with teeth sharp enough to damage nerves and blood vessels. If that wasn't enough, a number of barracuda have ciguatera toxin in their flesh, which can leave victims with nausea, hallucinations and other side-effects.

#10: Needlefish

Needlefish present an… unorthodox kind of danger. They’re not big enough to eat humans. They’re not poisonous. And they don’t get mad at us for territorial reasons. Nope. They’re just long, sharp-faced fish who are extremely curious about the lights in our boats at night. So curious that they’ll shoot across the shallows at 37 mph and leap out of the water to see what’s going on above decks. For the people on deck, that means a sudden barrage of fishy spears that fly out of the deep like the first shots of a war with Atlantis. Injuries can range from bites and scratches to pointy wounds if the fish’s beaks hit you hard enough.

#9: Stingrays

It may seem passive, but don't dare underestimate it. The stingray, typically relaxed, can hold its own and even do serious damage with its sharp spear-esque tail. Stiffening whenever the ray detects a threat, the tail possesses a serrated tip capable of severing arteries and is lined with venom that particularly endangers mammals. The stingray's sheer deadliness was tragically shown when, in 2006, wildlife expert and television host Steve Irwin was killed by a stingray's tail repeatedly striking him in the heart.


#8: Bull Shark

This might be a list of deadly ocean creatures, but bull sharks are actually at their most dangerous when they’re NOT in the ocean. Now don’t completely freak out. Sharks haven’t figured out how to come on land… yet. But bull sharks do swim inland, up rivers, and into lakes. Like most sharks, bull sharks aren’t all that interested in humans as prey, but they’re big enough that a curious nibble will put you in the hospital. Thanks to that increased proximity, bull sharks have attacked more humans than any species other than great whites or tiger sharks. They’ve harmed over 100 people and taken the lives of about 25.

#7: Cone Snail

Snails are soft, squishy slow-mo creatures that eat leaves and carry their little houses on their backs. How the heck do they end up on a list of deadliest creatures? Well, these snails are here for the venomous harpoon-like tooh they use to hunt their prey. Yes, venomous harpoons. It’s a cartoonishly evil-sounding weapon, sure. But it’s also deadly serious. Geography Cone snails in particular are the most venomous animal in the world, full stop. At least 30 people have had fatal interactions with cone snails. But the nature of being a dangerous animal that hides in a pretty shell on remote beaches means they could also be responsible for even more fatalities we don’t know about.

#6: Tiger Shark

The bull shark may be imposing, but the tiger shark is something else. This large shark has a reputation for attacking and eating anything – including smaller sharks – and is one of the sharks most frequently associated with fatal shark bites. Tiger sharks don’t seek out humans as food, but they do tend to linger in shallow waters and river mouths where contact with humans is most likely. What’s worse, their keen senses and calcified teeth allow them to make quick work of any prey they desire.


#5: Great White Shark

The adjective “Great” being in this animal's name is less a statement of positivity and more a grim tribute to its ferocity. The Great White Shark's most immediately recognizable quality is its size; they can grow to over 25 feet in length and weigh over 7000 pounds. However, these sharks have another notable habit: they strike at their prey from below with their mouths wide open, allowing their razor-sharp teeth to do as much damage as possible. It's no wonder that about a fifth of attacks by Great White Sharks are reportedly fatal, given the viciousness on display.

#4: Saltwater Crocodiles

Fear the crocodile, for it strikes when you least expect it. As the name suggests, the saltwater crocodile can very easily traverse open waters, allowing them to spread across Southeast Asia with terrifying ease. Saltwater crocodiles have been reported to have a bite power 10 times greater than that of the Great White Shark – at the very least, its large size and weight make it frighteningly easy to trap its prey. During a battle in World War II, hundreds of Japanese soldiers crossing through swampland in Myanmar were allegedly killed by saltwater crocodiles. Stuff like this gives us pause...

#3: Oceanic Whitetip Shark

As we’ve repeatedly stressed, sharks usually aren’t interested in eating people. But there’s one time when the normal rules don’t apply: a feeding frenzy. When there’s blood and commotion in the water, certain species -- like the especially aggressive Oceanic White Tip -- go into a swarm. And what causes more blood and commotion than a shipwreck? There have only been a handful of confirmed fatalities from white-tip shark attacks, but many shipwrecks and most castaways go unreported. If other wrecks played out like that of the USS Indianapolis in World War 2, we may never know how many human lives the oceanic whitetip has taken. But in the Indianapolis wreck alone, the estimated count was somewhere between a dozen and 150.

#2: Box Jellyfish

When it comes to the dangers of the sea, size matters not. Hence, we have the box jellyfish, a class of jellyfish that compensates for its small stature with a largely unparalleled sting. Those subjected to the venomous touch of the box jellyfish's tentacles are said to undergo extreme pain and a burning feeling. Box jellyfish venom is reportedly so potent that some people experience fatal cardiac arrest within minutes of being stung. The worst part is how hard it is to detect a box jellyfish before it can cause harm, due to its almost-transparent appearance.

#1: Sea Snake

And here we thought ordinary snakes had enough deadly surprises to offer the world. Alas, the sea snake – though typically nonchalant when it comes to other animals – still poses a danger thanks to its venom. On the rare chance that a sea snake, or coral reef snake, chooses to inject its toxin while biting a perceived attacker, a sizable list of symptoms are in store for the target. The after-effects range from elements of nausea to general aching and a tetanus-like ailment to even heart failure. It's a horrible fate delivered from an otherwise passive animal.
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What about sea scorpion?
What about an electric eel
When I go for a swim, everything is out there to kill me.
What about sailfish?