Mighty dragon meets his match

Dragons are known for having capabilities far superior to almost any other animal, and a particular darkish-green one was certainly no exception. With his near-impenetrable scales and abundance of muscle, he would often boast he was unbeatable, though he did still have his shortcomings. For one thing, it was plain to see that he was fairly small for a dragon, with the tallest human he'd encountered only being 2 or 3 feet shorter than him. He didn't really mind his size, though he had a particular weakness he was rather embarrassed about, and did everything he could to keep it secret.
Currently, the quadrupedal dragon sat on the edge of a cliff, about 30 feet up, glaring down at the only "being" that knew his secret: The ocean. More specifically, the water itself. No matter how hard he tried, or what strategies he used, he just couldn't figure out how to swim. Water seemed to be the only thing he could never beat, and it even gave his opponents an advantage as it would block his fire breath. Eventually, he accepted that water was, at least to some degree, better than him, and decided to instead work on somewhat reducing its threat to him. He could already see fine underwater, and trying to breathe fire there was hopeless, just resulting in a cloud of smoke-filled bubbles, so he practiced holding his breath. What started at a limit of roughly 20 minutes was gradually pushed farther and farther, and with months of work, his lungs caught up with the incredible capabilities of the rest of his body, giving him a new breath holding record of an hour and a half! Even among other dragons, that was an impressive time, and it gave him yet more reason to be proud of his abilities.
The dragon sighed. He wanted to someday swim in - or perhaps, hunt - a school of fish, but it didn't seem he would ever be able to. He got up, stretched, and started to walk away to go do something other than covet an ability to swim, but after just a couple steps, the ground started to shake. The section of cliff he was on was breaking away! With only a moment of surprise, he sprinted for more stable ground, but the part he was on was already sliding down, quickly sending him off balance and sliding after it on his belly, frantically clawing at the ground in an attempt to stop himself, but now his neglect of his claws was coming back to bite him. He didn't often worry about keeping his claws sharp, they couldn't really do anything his strength and teeth could. Except, obviously, keep himself from sliding, which hadn't really come up before.
While his sliding was slowed down, it wasn't stopped, and within seconds the dragon fell from the cliff entirely. He yelped in fear, then gasped deeply and puffed his cheeks as he plummeted into the ocean below with a loud SPLASH! The impact stung a bit, but it would take more than that to actually injure him. Instinctively, he flailed and tried to swim up, but just sank like a rock, like always, quickly giving up on it and letting himself sink. For a moment he was more embarrassed than afraid, hoping no one had seen his clumsy fall or heard his yell, before he looked down at the distant seabed he was slowly approaching. While he sometimes enjoyed going for underwater walks, despite not being able to swim, it was rare that he went to this kind of depth. Eventually, he settled onto the bottom, and looked back at the surface. It had noticeably faded with his depth, and he could tell this was the deepest underwater he'd ever been.
Not wasting any more time, he looked around for any possible way to climb out, noticing he'd landed in a more open section of a trench and that he was surrounded by sheer walls on every side but one, which had a decently-sized opening leading farther into the trench. With hope that he'd eventually be led to an escape route, he walked through the opening, letting out some bubbles with a bit of a smirk as it was finally being proven to him that his breath holding practice hadn't been pointless.
A very long time passed before anything interesting happened. The dragon walked and walked and walked, occasionally coming to a branching path and picking one at random, then sometimes doubling back and picking another after finding a dead end. Over half an hour went by like this, long enough that by now any average dragon would either be choking or already fully drowned, but this one still had a tight hold of his breath and showed no obvious sign of needing more. Still, he was beginning to feel the need to breathe, and soon started blushing from the strain.
Eventually, the dragon found a particularly rough-looking wall that stretch far above him, seemingly all the way to the surface. Despite the sorry state of his claws, he propped his front paws onto the wall and tried to climb up. He got a few feet off the ground, but soon started to slip, scrambling to even stay in place, the red of his cheeks overtaking the rest of his face before he got tired and had to sink back down. There was no possible way he'd be able to climb this wall, and while he looked up at it, his chest heaved and he awkwardly brought his front paws to his muzzle, cheeks noticeably swelling a few inches. That attempted climb had used more energy than he realized, and likely cut a few minutes from the time he had left before he'd end up being forced to breathe. With no other options, the dragon pressed on, leaving the almost-scalable section of wall behind.
Another half hour. His blush had become purple, each of his cheeks now bigger than his entire head, and his lungs were just starting to burn. A few minutes ago his path had led him to a cave, which he, of course, entered. The ceiling above didn't frighten him, it wasn't like he could swim for the surface anyway, but he soon noticed something odd about it: There was an air pocket above him. Again, it didn't matter, but on the off chance it was being supplied from below, he had to find its source. With five minutes of searching, he did! A sort of blocky stone funnel jutted out from the cave floor, occasionally spurting out large bubbles, some of them bigger than the dragon's entire body. One came out and floated away as he approached, so he sat next to the "bubble vent", as he'd be calling it, and waited for another. It only took a few seconds, and a bubble a bit bigger than his head popped out with a bloop, the dragon opening his maw wide to inhale it, swallowing a little seawater in the process. Still, with an air bubble of that size, his lungs were fully refreshed and his confidence restored. Once again, he set off to find a way to the distant surface.
Finding another way out of the cave after a little while, the dragon was back outside again. And, once again, very little happened for some time, though not as long as before, only about 16 minutes after leaving the cave. He didn't notice at first, but he wasn't alone; a great white shark stalked behind him, unaware of what dragons were and thinking him an easy meal. Soon, it lunged towards him, cutting through the water with enough speed to be audible, catching the dragon's attention. He had just long enough to turn his head and see the shark clamp down on his back right leg, and while it didn't get past his scales - he truly believed there was nothing that could - it still hurt, and he gave a bubbly yelp of pain. Quickly catching himself, he closed his mouth again, the shark continuing its useless attempts to eat him. It was more of an annoyance at this point, and as the shark released him, he gave it a brutal kick, with so much force it was instantly knocked unconscious. That would certainly teach them not to mess with dragons! Although, having lost some air with the shark's initial bite, the dragon already started blushing again, and tried to hold his muzzle shut for a moment, cheeks puffing back to the size of his head. He didn't go back to the cave's bubble vent, though; having almost effortlessly triumphed over one of the seas' strongest creatures gave him even more confidence, and he decided not to go for more air, as it would hardly make a difference.
Onward he went. This time there were no interruptions, and the next half hour passed uneventfully. By the end of that, the dragon's cheeks had turned purple again, but there was no air to be found this time, and he simply held on as best as he could. He soon came upon another promising-looking wall, and tried to climb it again. While he got quite a bit of height this time over a few minutes of climbing, his large cheeks made it even more difficult than last time, and he eventually slipped from the wall just like the last. Not even giving it a second look, he just continued on and left this one behind as well.
20 minutes later, the dragon's lungs neared their limit. A fierce burning had taken hold of them, and his now blue cheeks exceeded his head in size again. He definitely wasn't as confident any more, but he took pride in having held his breath this long. Yet more walking awaited him, and although his body shivered and begged for air, the dragon kept going. After all, the air wasn't exactly going come to him, he had to hope he'd find another bubble vent before it was too late.
The next minutes were the slowest yet. The breathless dragon struggled on, vision starting to blur as he bubbled and let out pained whines and whimpers. His overtaxed lungs seared with carbon dioxide, feeling even hotter than his own fire breath! Finally, he had to stop, covering his muzzle once again. His body repeatedly jolted and shook, and he tightly shut his eyes, his cheeks getting even bigger. This was it. He may have been incredible at holding his breath, but he didn't have gills, and even he could only hold off the inevitable for so long. For the first time in years, the dragon was terrified, as his lungs gave up at last and his paws lifted from his muzzle.
A cloud of bubbles erupted from his maw as it opened wide, and the dragon's terror turned to full-blown panic. More and more bubbles gurgled from his exhausted lungs, even in the moments he managed to force his muzzle closed. He managed to at least slow down his instinctual exhaling, and it was a surprisingly long time before his lungs were completely empty. They remained that way for a few seconds, the dragon's mouth hanging open, before going wide again as a torrent of water surged down his throat. He tried to swallow, but it was already too late, and the burning of his lungs somehow got even worse as water filled them. Loud choking and gargling echoed off the trench's walls, the dragon falling to his side as he frantically thrashed about. Mercifully, the pain didn't last all that long, and only about 30 seconds after his first breath, he'd already calmed from his desperate gasps to heavy panting, and managed to struggle to his feet.
His mind felt fuzzy, but he still knew he had to keep moving, and awkwardly continued his walk. Now that it wasn't hurting any more, breathing water actually felt better than he'd expected. While it still felt pretty awful, he could see why some strange folks enjoyed it. His flooded body moved slowly and continually hiccupped, but it held on despite the dire lack of oxygen. He made little progess over the next few minutes, getting increasingly dizzy and sleepy as his panting slowed to calm breathing. With a sudden weak gasp, he held a breath of water and puffed his cheeks again.
As his walking became more akin to stumbling, the dragon released his aquatic breath and his eyelids fluttered as he started to lose consciousness...But, he forced himself to stay awake, barely able to feel anything any more. Then, he saw something that tore away what little hope he had left: He'd hit a dead end. At this point, he had no chance to even get back to the last junction, let alone find more air. So, he gave up. Totally exhausted, the drowned dragon fell to his side, briefly shuddering before closing his eyes and allowing himself to pass out.
At last, his nemesis, the water, had defeated him.