1. They probably just found a floating barge and looted it. Barges are used in modern times to transport thousands of tons of cargo and that cargo can be anything from guns, to ammo, to alcohol, to cigarettes. When they raid the atoll, the Deacon asks if there are any smokes on it. There are none, but he wouldn't be asking if they were impossible to find. Clearly it's something they've found in the past. It's just that now the atolls are less common as everything is rusting, sinking, etc
2. If he's using modern ammo, then the ammo is watertight and the gunpowder would not get wet. So yes, the gun could work. Some guns even fire underwater. You're thinking of black gunpowder weapons with exposed gunpowder. That indeed would not fire.
3. The gills don't matter. He would only be able to breathe underwater with them. Phytoplankton produce most of the world's oxygen anyway and they live in water. If anything, the air quality would be better since there would be far less industry expelling pollutants into the atmosphere.
4. Oceans have a major impact on climate. You've never heard of the connection between the ice caps melting and climate change?
5. Their base is an oil tanker and they distilled the oil. Distillation is not an impossible process and they had the oil not just to distill but also to use as energy to produce heat needed to distill the rest of the oil. In fact, I think they showed this in one of the scenes. They can't refine it completely, which is why they "smoke" and are called "smokers."
6. Did they resurface quickly? They cut to the part when they surface, but everything in the movie indicates they spent a long time down there. Enola got bored and the smokers had time to approach the Mariner's boat, completely surround it, board it, lay a trap for him, and hide. The Mariner spent decades diving and likely knew about decompression sickness from a combination of personal experience (having survived minor cases of it) and the numerous magazines he had stored on his boat.

It's true that if the ice on the polar caps melted, the ocean would only rise and cover our current coastlines. But we are currently under a major crisis of losing a large amount of our topsoil from erosion. This is the result of unhealthy farming practices, excess construction, mining, etc. It's all just draining down the rivers into the oceans. The movie never says the year it takes place so theoretically it could be set hundreds of years in the future. Whether these factors would actually create a water covered world is debatable. I enjoyed the movie as science fiction/fantasy.

I must have missed the message at the beginning of this film that stated "what you are about to see is all based on concrete facts"?????????

3.Nearly no dry land = nearly no vegetation = no oxygen to breathe The Mariner could because he had gills but noone else
Tiny ocean plants called phytoplankton contribute 50 to 85 percent of the oxygen in Earths atmosphere.

How come everyone starts turning into beep google scientists whenever a sci-fi movie comes out? You just show your ignorance. Practically every action movie Hollywood has ever produced is full of physical impossibilities. Complaining about something you had to read post-viewing just to make yourself feel smart does exactly the opposite.
Amy
:
I swear to GodI swear to God! That is NOT how you treat your human!

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I've just read all of this and confess that I am baffled. This movie is fiction, SCIENCE fiction. When I think of all the 'plot holes' you could all find (and rant about) in the endless number of scifi books from the past. and, gosh, if you were reading them back then you'd be listening to the endless disdainful commentary of persons who said 'impossible', 'preposterous', 'not scientifically probable', 'unrealistic', blah blah. Go to the moon? space travel? drones? Computers? AI? All previously science fiction. And we didn't dissect it, we just admired the minds that created it. And lived in those worldsand wordsfor awhile. That's what fiction is for.
This isn't a 'film', it's an adventure. Hey, just fall into that!
ps: we now have people dressed only in body paint and a g-string - heinlein would be so pleased!

3: No. This is a common misconception. Let's take the example of Amazonia: lots of trees produce lots of oxygen, which is then used by said trees (who also breathe), and every living creature in the rainforest Basically, in terms of quantity, the amount of oxygen produced by trees in Amazonia is equivalent to the amount of oxygen consumed by Amazonia.
4: Huh Why do you think the ice-caps melted? Global warming! Hence, Everest is warmer because all of Earth is warmer (plus every other reason given by other posters).

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Wow, you're an idiot.
For starterslearn WTF a PLOT HOLE ACTUALLY ENTAILS. A plot hole is when one characters is blown up in a nuclear explosion at ground zero and then shows up unscathed to stab the villain in the back at the end of the film. Something unlikely or hard to believe is NOT A PLOT HOLE. A plot is a story-line. Something unlikely is just that.very unlikely. A plot hole is when something happens that is otherwise impossible to the story-line as proposed.

1. Ummm, where do they come from now? If anything, if the world were crumbling and sinking underwater, hoarding of munitions would be a key and common place event as law fails around everyone. Guns and ammo, gasoline, water, and canned goods would be involved in almost any major event. In this case, obviously boats and yachts would be key targets too.
2. It's a world covered with water, is it so hard to believe that they've modified weapons and rounds to avoid water trouble?
3. You fail Biology 101. In fact.the majority of the worlds oxygen comes from the ocean, not land-based plant life. It's algae and shallow sea-floor vegetation that help produce so much of our breathable oxygen.
4. I think you somehow managed to avoid the beginning of the film. Global warming caused the ice caps to melt. That led to the water rise. In the future, it will still be hotter, even high up. That means globally higher temperatures.even on Mt. Everest. Did you see icebergs?
5. First of allgasoline is REFINED from crude oil.NOT distilled! Wow. Secondly, even crude oilburns. It may not be great for engine health but even modern engines are capable of burning bio-fuels. We also don't know that they were not capable of refining oil in some manner. Heck, the Mariner had a small contraption that could refine clean water out of his own urine. This was a hint that they could likely do the same with oil.
6. Suspension of disbelief, derrp. They often fire more bullets than a gun can hold, one rope would hardly making a bungee cord for about 300 lbs. of people, and what are the chances when they find dry land that they stop on the shore within walking distance of the girls' dead parents' hut?
   Aristophanes once wrote, roughly translated

there is no "probably" about them being able to refine their oil, since when the deacon opens the hatch and the old guy says something like there is only 4 and a half feet of crude oil left, the deacon then says to his buddy "how much is that when we refine it" and his buddy says something about not being enough to run their fleet for long leading the deacon to make the decision to cancel all outings except to hunt the girl
so yes, its explained

If that squiggly machine can change piss to drinking water, it can probably do the same to seawater.

goddangit folks, it is NOT a plot hole for a fictional film to show us things that are different than actual world facts. It's like putting a big flashing sign over your head saying, "I do not get fiction".
http://www.rateyourmusic.com/~JrnlofEddieDeezenStudies

Re: Number 4. I think the implication was that the polar icecaps had been melted by rising temperatures, which would turn even the coldest places on Earth (such as the peak of Mt.Everest) into warmer climes. Hence why everywhere in the film seems to have a tropical climate.

"Margin for error: The premise of the film is obviously that sea levels have risen drastically putting the survivors a good few hundred metres above current sea level. This in turn means that the air they breath may be thinner and that they will have adapted to needing less O2."
Actually if overall sea level rose, wouldn't that effectively "raise" the atmosphere, with pressure at the new sea level not changing much, if at all, from current sea level air pressure? The reason air pressure varies by altitude is that most of the mass of our atmosphere settles at the lowest elevations it can (sea level, and areas below sea level where they exist, such as California's Death Valley) due to Earth's gravity. So it would settle at a similar pressure gradient from the new lowest elevation, since Earth's surface gravity wouldn't change (or more technically, would change
very, very
negligibly due to an increased distance of a few km from the core).

The decompression sickness is caused when a oxygen and gases, compressed by water pressure, expand in the lungs, blood and body as the diver rises to the surface. You can imagine the result. I gather that since the air in their make-shift diving bell was not compressed, then the problem of decompression sickness was not an issue
That is physically impossible. If the air in the diving bell was not compressed then basic physics throws up two problems both of which relate to Boyle's Law. wikipedia it or try this: inflate a balloon and take it down to the bottom of the deep end at your local pool. Notice how the balloon shrinks as the volume of air inside decreases. The deeper you go the greater the pressure on the air so it has a smaller volume.
The problems are:

1. The pressure of the water would crush the diving bell. Unless the diving bell is made of some magical super strength material that can withstand that kind of pressure. Nothing in the movie suggests this however let's let that one slide and assume that this bell can withstand the depths shown. It has absolutely no pressurisation or air supply of it's own meaning that it leaves the surface with a fixed amount of air and once that's gone it's gone. That in turn means:
2. Decompression would not be a problem anyway because she would have died from lack of oxygen. Let's say that the sunken city was 200 metres below the surface (which it was quite comfortably more than). The pressure at 200m depth is 21 bar (i.e. 21 times the pressure on the surface.)*. Which means you would use up 21 times the amount of air in one normal breath that you would on the surface. For example an average healthy adult has a lung capacity of around 6 litres, of which 4.6 litres is used in normal respiration when not undertaking strenuous activity. breathing 12-16 times a minute, again a normal rate when standing still not exerting yourself, you will use at least 43.2 litres per minute. At 200m that will increase 21 times to 896.2 litres per minute.
   For her to survive let's say ten minutes in the bell at that depth there would need to be at least 8962 litres of air in the diving bell when it left surface (this is if you discount the time spent descending/ ascending).
   That diving bell looked to be only just plausibly 10,000 litre capacity but then I never got a good look at the available space inside so it could well have been less than that but either way it would be a very close thing.
   When you add on the time needed for deco, which would be considerable, it's highly implausible that there would be enough air in the bell for her.

• Margin for error: The premise of the film is obviously that sea levels have risen drastically putting the survivors a good few hundred metres above current sea level. This in turn means that the air they breath may be thinner and that they will have adapted to needing less O2. The difference would be insignificant unless you're talking about them being a few kilometres higher than we are. However if that's the case it also means they descended a few kilometres meaning the air in the bell would be reduced from 10,000 litres to at most 1,000. It also means she would be breathing at least 4320 litres per minute so the maths there are self explanatory.
  The only way for the diving bell to have enough air is if it were pressurised in the same way as a submarine which, as mentioned, has an in built system for keeping the air pressure the same as that on the surface. However it is painfully obvious from watching the scene that this diving bell has no such system.

Just watched this again
Who cares about plotholes
This movie is just great fun
It's a comic book fantasy.
Enjoy the jokes, the beauty, the excitement
Dennis Hopper is just a stitch, as are others

5. Where did they get the gasoline for the jetskis? There was crude oil shown in the smokers boat but you would need to distill it
   In the scene where we first see the pale guy in the smoker's ship with all the oil, refining the oil is mentioned by either Deacon or one of his lackeys.
   Mother, as first lady of the American stage Helen Hayes once said, "I'm going to kill you."

Hey, I think you are confusing 'plot holes' for 'questions'.
1.Where did they get guns and ammo from?
Where did they get ANYTHING from? Probably where they got the oil from and the BOATS. All they needed to find was some gun-freak's 'end of the world' stash of weapons .. or two.
2. How can the Mariners shotgun work after being submerged?
Many guns work after getting wet or submerged. I guess hollywood did you wrong by showing you too many outdated myths.
3.Nearly no dry land = nearly no vegetation = no oxygen to breathe The Mariner could because he had gills but noone else
Well he'd still need O2 because all gils do is extract the O2 from the water. However, as said above, algae also photosynthesises, and there is a LOT of it.
4.The whole world being covered by water wouldnt make the top of mount everest any hotter.
It would change the temperature incredibly, just as said above. Think about how 'high' a lot of islands are already. DROP the water and see some HUGE mountains
5. Where did they get the gasoline for the jetskis? There was crude oil shown in the smokers boat but you would need to distill it
They had crude oil, but they could also have stolen a lot of gasoline too. Actually, he uses the word 'go juice' and also 'black stuff' as proper-nouns. Perhaps he was talking about the two different things. Anyway, if you are watching a film and wondering about how they distilled crude oil into gasoline, then seriously, LEARN how to watch a movie properly.
6.How did the woman not die from the pressure after being submerged several hundred feet underwater and resurfacing quickly?.(Yh I know it would be an anti-climax for them to go up extremely slowly)
The decompression sickness is caused when a oxygen and gases, compressed by water pressure, expand in the lungs, blood and body as the diver rises to the surface. You can imagine the result. I gather that since the air in their make-shift diving bell was not compressed, then the problem of decompression sickness was not an issue

By far the biggest plot hole in the movie is the melted polar ice raising the ocean several hundred (or thousand) feet. As previously mentioned, in reality it would only rise a few feet. However, I'm willing to forgive this exaggeration because it provides the setting for the story. A better solution would have been to leave the exact cause of the deluge ambiguous, but whatever. I can handle intentional unbelievable plot points (all movies do it to varying degrees), but the rest of the world outside of that main fantasy element has to function like it should for me to really admire a movie.
Most of your points have been satisfactorily answered, but here's my input:

1. They stole the guns from atolls/ships that they raided. This applies somewhat for the ammo as well, but they do make their own rounds. This is quickly shown in the theatrical version and moreso in the extended version.
2. Some weapons are watertight by design. Other just have diminished performance when wet. One of these things must apply to
   Ulysses
   ' shotgun.
3. Most of the oxygen on earth is produced by undersea vegetation. Every forest on the planet could burn to the ground and we would still be able to breathe (assuming the ocean plants weren't contaminated and we didn't all die from smoke inhalation). Since the forests of Waterworld were drowned, we would presumably have no respiratory side-effects.
4. Yes, it would. Everest's peak would be the new sea-level and have the applicable climate thereof. The earth would become a relative greenhouse compared to what we know.
5. Similarly to #1, they could probably refine their own fuel. Although it would be quite poor by our standards; producing tons of smoke and fumes (thus, Smokers) as well as burning up quickly. I also doubt it would be of aviation grade (no planes for you!)
6. I don't think decompression sickness occurs unless you have direct exposure to the pressure (IE: scuba diving) since submarine crews in their sealed vessel do not have to worry about it. It could be argued that the bubble protected Helen from suffering the effects of the bends. However, a better question would be why the enormous pressure didn't cause the whole thing to implode.

1. This isn't a plot hole since it's a question. The fact that we don't know how something is possible doesn't mean it's impossible.
2. Same as 1.
3. Unsupported assumption. We can only speculate on what would happen if the earth were entirely flooded, and there may be other conditions to take into account before judging that something is impossible. Because of that, the conclusion that it's a plot hole is false. Just for the sake of speculating: nothing suggests that the oxygen left over from before the flood, along with the amount produced in the remaining land, wouldn't have been sufficient. Also, if the mariner had time to develop an aquatic respiratory system, for all we know it's possible the other people would have developed some sort of respiratory system that relies less on oxygen and more on other minerals.
4. Unsupported assumption. There's no evidence that everything at or above the altitude of earth's highest point would be at freezing temperature just because the terrain is frozen at said point.
5. Same as 1.
6. Same as 1.

the bubble he had her in protected her if the bubble had oxygen in it she would not be pressurized the oxygen in her lungs would protect her

The summary stated the underwater city was denver, CO, so it had a higher elevation to begin with.
The wild, cruel animal is not behind the bars of a cage. He is in front of it.

1. It had probably been saved up. There are more guns in this world than there are people.
2. Algae could produce the oxygen. There was also hardly any animals or people left on the world, so the few breathing lifeforms left were probably sustained by the algae.
3. The only reason Mount Everest is cold is because the atmosphere is thinner. If the water level elevated, so would the atmosphere.
4. This is a true "plot hole" by definition - we just have to assume they had some method of refining the crude oil.
5. It wasn't just several hundred feet of water, it would have to be several THOUSAND feet of water mount everest is 30,000 ft tall, which is where they end up in the end.. The pressure from 20,000ft +/- a few thousand feet of water would KILL YOU.
   TOO MUCH HAIR!! CANNOT SEE!! CANNOT SEEEEE!!!