In The Deep Deep River is a poetic TTRPG about diving and scavenging. Think Abzu or I Can Hold My Breath Forever or Subnautica, but in tabletop form.
The PDF is 11 pages, with well composed photo art and a clean, readable layout.
Setting-wise, Deep Deep River isn't anchored to a particular world. You can run anything from Low to The Ocean Hunter. The thing that matters is that there's an abyss, and the player (or players) dive into it.
Mechanically, you resolve checks by rolling a pool of d10s and trying to match a target number. You start with two dice, but can gain extra by finding moments of calm in the narrative. Your dice pool can also shrink as you encounter hardship.
Deep Deep leans on the GM being experienced, and if this is your first TTRPG you're maybe going to get a little bit lost here. There's plenty of philosophy for running the game, and there's a table of prompts at the back of the book, but the GM needs to know when to offer good and bad significant events, and needs to know how to establish and maintain a compelling atmosphere.
Overall, if you want a oneshot or short campaign game about water, depth, and searching, this is a solid engine for that. It's really focused on pacing, and the sparseness of its mechanics highlights the importance of the player's breath and calmness. If you like rules-lite, mechanically-driven storytelling, or if you like thinking about what lies underneath oceans, give this a chance.
-I couldn't figure out what the default target number is. I might've missed this in the text.
-Having to exactly match, rather than match or exceed, the target number makes succeeding rolls a bit tricky with your starting dice pool, which in turn can make it difficult to avoid a cycle of failures and dice pool reductions. The GM kind of has to feed you a few dice before things can get scary or intense.
-Can your dice pool be reduced below its starting level?