Hypothesis - Before Percy found out he was a demigod ("ignorant-Percy") he could not breathe underwater and would have drowned in an emergency.

  • One of the instances of an irrational fear crippling a demigod is with Thalia, whose fear is first introduced in The Titan's Curse. In one of the Heroes of Olympus books (can't find quote), Percy muses that if Thalia wasn't so afraid of heights, she could probably fly just as well as Jason. Presumably in the same book, Percy worries that his dreams of drowning in inky-black water are like Thalia's fear - if he truly believes he cannot breathe underwater, then he would drown. This supports the hypothesis.
  • In the Lightning Thief, Percy discovers he can breathe underwater after jumping into the Mississippi River. Here we hit a hole in the hypothesis - this Percy is apparently ignorant of his ability, but is able to breathe underwater, disproving the hypothesis. However, Percy has already learned of his special connection with water, and uttered a prayer to Poseidon ("Father, help me.") before jumping. Perhaps in the moments before letting go of his breath, he trusted his father to save him and thus let go of his fear. He thus believes that through some way or another, he cannot drown. This does not disprove the hypothesis, as Percy is not fully ignorant.

Let's assume that before the events of The Lightning Thief, Percy is on a ship that goes down with all hands. In a typical holier-than-thou fashion, Poseidon does not react in any way. Can Percy breathe underwater?

  • Poseidon wasn't reacting because he (with Zeus and Hades) wasn't supposed to be having any children. – user40790 Jun 30 '16 at 22:21
  • lol, I understand why all the gods acted that way, but I was just trying to be funny. Hurr hurr hurr. – allies4ever Jul 2 '16 at 3:57

I am going to say no.

As a previous answer has stated drowning is due to lack of oxygen to the brain and ultimately the brain dies. Drowning is defined as respiratory impairment from being in or under a liquid. Also as wiki states in classified as death, ongoing health problems and no ongoing health problems.

Oxygen deprivation A conscious person will hold his or her breath (see Apnea) and will try to access air, often resulting in panic, including rapid body movement. This uses up more oxygen in the blood stream and reduces the time to unconsciousness. The person can voluntarily hold his or her breath for some time, but the breathing reflex will increase until the person tries to breathe, even when submerged.

The breathing reflex in the human body is weakly related to the amount of oxygen in the blood but strongly related to the amount of carbon dioxide (see Hypercapnia). During apnea, the oxygen in the body is used by the cells, and excreted as carbon dioxide. Thus, the level of oxygen in the blood decreases, and the level of carbon dioxide increases. Increasing carbon dioxide levels lead to a stronger and stronger breathing reflex, up to the breath-hold breakpoint, at which the person can no longer voluntarily hold his or her breath. This typically occurs at an arterial partial pressure of carbon dioxide of 55 mm Hg, but may differ significantly from individual to individual and can be increased through training.

The breath-hold break point can be suppressed or delayed either intentionally or unintentionally. Hyperventilation before any dive, deep or shallow, flushes out carbon dioxide in the blood resulting in a dive commencing with an abnormally low carbon dioxide level; a potentially dangerous condition known as hypocapnia. The level of carbon dioxide in the blood after hyperventilation may then be insufficient to trigger the breathing reflex later in the dive and a blackout may occur without warning and before the diver feels any urgent need to breathe. This can occur at any depth and is common in distance breath-hold divers in swimming pools. Hyperventilation is often used by both deep and distance free-divers to flush out carbon dioxide from the lungs to suppress the breathing reflex for longer. It is important not to mistake this for an attempt to increase the body's oxygen store. The body at rest is fully oxygenated by normal breathing and cannot take on any more. Breath holding in water should always be supervised by a second person, as by hyperventilating, one increases the risk of shallow water blackout because insufficient carbon dioxide levels in the blood fail to trigger the breathing reflex.

A continued lack of oxygen in the brain, hypoxia, will quickly render a person unconscious usually around a blood partial pressure of oxygen of 25–30 mmHg. An unconscious person rescued with an airway still sealed from laryngospasm stands a good chance of a full recovery. Artificial respiration is also much more effective without water in the lungs. At this point the person stands a good chance of recovery if attended to within minutes.

A lack of oxygen or chemical changes in the lungs may cause the heart to stop beating. This cardiac arrest stops the flow of blood and thus stops the transport of oxygen to the brain. Cardiac arrest used to be the traditional point of death but at this point there is still a chance of recovery. The brain cannot survive long without oxygen and the continued lack of oxygen in the blood combined with the cardiac arrest will lead to the deterioration of brain cells causing first brain damage and eventually brain death from which recovery is generally considered impossible. The brain will die after approximately six minutes without oxygen but special conditions may prolong this. Obviously there is some magic involved in Percy being able breath under water and as another answer states, he probably has some mechanism that enables him to get the oxygen from the water.

As for Hyperventilation, this is what Wiki state on Hyperventilation

Hyperventilation occurs when the rate and quantity of alveolar ventilation of carbon dioxide exceeds the body's production of carbon dioxide.1 Hyperventilation can be voluntary or involuntary.

When alveolar ventilation is excessive, more carbon dioxide will be removed from the blood stream than the body can produce. This causes the concentration of carbon dioxide in the blood stream to fall and produces a state known as hypocapnia. The body normally attempts to compensate for this metabolically. If excess ventilation cannot be compensated metabolically, it will lead to a rise in blood pH. This rise in blood pH is known as respiratory alkalosis. When hyperventilation leads to respiratory alkalosis, it may cause a number of physical symptoms: dizziness, tingling in the lips, hands or feet, headache, weakness, fainting and seizures. In extreme cases it can cause carpopedal spasms (flapping and contraction of the hands and feet)

What eventually happens is you most likely pass-out due to the easiest way to get oxygen to the brain is on the floor and the body use involuntary reflexes to return the bodies breathing to a state where it can survive. I don't know how many documented case of people dieing from hyperventilation, but it is very small and there usually is complications.

So, going back to Percy, even if he were to panic, he would eventually pass out and his involuntary reflexes take over to resume normal breathing and as he is able to breath under water, he would then therefor not die.

Resources, I am a medical physician.

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    Hey i didnt think of it in this way but it totally makes sense. once percy faints, his default demigod mode will save him. but what if thalia were to faint while free falling from a height? would she then stop falling and just float in space? or is it a special power that all children of zeus need not have? – Dev Jul 2 '16 at 14:50
  • @Dev - I suppose it would depend if flying were something that can be done involuntarily, while unconscious. Breathing definitely can be, so passing out would help Percy. But flying seems to me more like something that has to be done actively - in which case, anyone who could fly would find themselves in trouble if they ended up unconscious in midair. – Megha Jul 3 '16 at 9:57
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    @Dev - I agree with Megha. We see that in the Blood of Olympus, Jason falls unconscious due to Piper's charmspeak when they're flying through the air and fighting Gaea (Piper tells Gaea to sleep, and affects Jason too). Jason then falls through the air. I don't know about drowning, but this definitely shows that flying is less of an Astro-Boy-type defense mechanism and more of an active ability. Still a thought-provoking answer, let's resolve this discussion and I might mark this one as the answer. – allies4ever Jul 7 '16 at 15:05
  • @allies4ever I forgot about Jason falling. Yeah , so it means that Thalia just doesn't have the power of flying. or she is too afraid to test if she does. But Percy does have the power. So I guess even if he drowned before he came to know of his powers, he would still not die. – Dev Jul 8 '16 at 5:57

The answer is no and yes, but not what you think. Drowning is caused by the brain being oxygen deprived, not having water in your lungs. You technically drown when you are choked to death and when you drink alcohol. He can breath under water automatically via magic (probably converting water to oxygen or something like that). However, he has been mentally taught that he can't breath underwater and fear can cause things like Hyperventalation which can cause oxygen deprivation which in turn can cause him to drown if he doesn't snap out of it.

So yes he can drown, regardless of any other other stuff, whether recognized or not. If he were to hyperventilate or something and couldn't recover he'd drown all the same as anyone else.

The no part comes from we actually know that his powers are not reflective of whether he's been recognized or not by Poseiden nor whether he knows he's a demi-god or not. We see this with the reading and understanding greek thing and we see it with this in particular. There are times it is mentioned that Percy liked sitting at the bottom of pools either in the first movie or first book and he'd get lost in just sitting there for what seemed like a long time that it is implied that he ignored as just his imagination. So we see that he uses his powers before he even knows about them and so...

The answer to your question is, no, Percy would not drown, just because he didn't know he is a demi-god.


As far as i remember reading it, Thalia was afraid of heights. Its not because she didn't know she was a demigod. So if Percy had a fear of water or of drowning,(I think it's called Aqua-phobia?) then he could die as we see in son of Neptune book where he is sucked into a bog and his powers were also not working properly. So i guess that means Percy wouldn't have died even if he didn't know he was a demigod but rather he would have died if he was phobic like Thalia. Also, I don't think Percy might have died in your hypothetical scenario because even if he didn't want to recognize him as his son, he would have helped him indirectly through naiads or some other sea creatures.

  • My main hypotheses covered ignorance in general - this includes not knowing you're a demigod but also loosely covers fears - like Thalia is ignorant of her ability to fly because of her irrational fear. My hypothetical scenario just had Poseidon be absent for any arbitrary reason - maybe he's off fighting a war, but I just wanted the reader to assume that Poseidon can't help Percy directly or indirectly, like he may have done at the Arch. – allies4ever Jul 2 '16 at 3:54
  • Thalia maybe ignorant of flying because she never tried because she was afraid of flying. but Jason didn't know he could fly too and yet he flew. that's why fear is more important factor (everybody is afraid of things like falling drowning snakes etc etc but actually being so phobic that they are rendered immobile and brain dead is different) or maybe Thalia just didn't have that power. is it definite that all children of Zeus should have the power of flying? – Dev Jul 2 '16 at 15:00

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