"I'll meet you at the bottom, take as long as you need", Blubby said with some strain as he mostly held a massive breath, before refilling what air had been lost by talking and then diving into the water with a splash, quickly sinking out of view. Ril, a lizard, stood on the edge, breathing deeply for some time before diving down to follow Blubby. It was fairly far down, though far from being an issue for either of the two divers, despite one not being capable of swimming.
Blubby was sitting on the seabed, looking about, when he noticed Ril swimming down toward him, and stood up. Ril waved to him, and the two set off toward a nearby cave to explore inside. For some time, there wasn't really much to see, an eventual steep vertical section slowing their progress. At least, it slowed Blubby, who couldn't simply swim up and had to climb, taking about a minute and a half to reach the top. Ril stuck around during this, not planning on leaving his friend behind in an unfamiliar cave, even though he was starting to need to breathe.
Thankfully, Ril's lungs wouldn't remain unsated for long, as an air pocket became visible down the next tunnel. He quickly swam to it to breathe, and while it would still be hours until it was necessary, Blubby joined him, propping himself up on a wall to get at least his nostrils above the surface. With another deep breath from both of them, they submerged once again and continued their exploration.
Before much longer, they reached the end of the cave, and it seemed their efforts paid off; there was a ton of gold coins, and even a small treasure chest! Blubby happily scooped up some coins in a paw, though soon put them back as he didn't really have a way to carry them without it being significantly harder to get around, and Ril picked up the chest, which was heavy enough to prevent him from swimming, so he began to just walk instead.
After another break to refresh at the air pocket, Ril and Blubby started to make their way back outside. The sloped section was far easier to traverse this time, as the two could simply jump and let themselves sink to the bottom, and they were past it in only a few seconds, soon leaving the cave into the open ocean. Carrying the chest was taking a fair bit of effort from Ril, and he was already feeling the need to breathe again, which started to be an issue before much longer. Blubby noticed Ril starting to lag behind, and could tell how badly they were in need of a breath, but without an air pocket nearby, they'd have to go all the way to the surface... Well, if Blubby didn't have a certain ability that would be perfect for this.
He motioned for Ril to stop, turning around and opening his mouth as he started to exhale. Instead of a stream of bubbles, however, a single bubble expanded from his mouth, growing to the point that it was a bit bigger than Ril's head. Ril smiled and set down the chest, grabbing the bubble that Blubby had made and inhaling it, exhaling from his nostrils partway through as the entire bubble was too big for his lungs by a fairly large margin.
With Ril now refreshed, the two continued on, walking up a gentle slope that eventually brought them to the surface. After some time drying off and enjoying finally getting fresh air again, Ril set down the chest and opened it to find it was packed full of gold coins, and even some gems! Blubby wagged his tail in excitement at the sight of this. Their dive had been more than worthwhile, and they'd definitely be coming back for the rest of the coins they'd left in the cave.