Inundated

🌊DO NOT ENTER WORLDS THAT YOU DO NOT WANT TO FLOOD - THE NEW CHUNKS WILL BE AUTOMATICALLY FLOODED

ABOUT

Inundated injects chunk generation and fill with water your overworld, nether and the end dimensions from Y 320 to -64.
It injects at the very end of chunk generation, meaning biomes, terrain, ores, and structures stay untouched.

Basically, all air and cave_air blocks are replaced with water, and all waterloggable blocks are properly waterlogged.
This keeps leaves, slabs, fences, and other blocks visually consistent underwater.

And yet - torches, sugarcanes, nether vegetation left as a feature and grass/flowers will eventually flood itself and dropped as item. (does all of this need to be replaced with water too?)

Inundated turns the game into a unique survival challenge, where you're forced to adapt to living entirely underwater — and figuring out how to live, explore, and build while everything is submerged.

NON-GENERATION FEATURE

There’s also a legacy command:

/inundated start/stop — it floods nearby chunks manually. (OP only)
This is useful for non-flooded chunks that were generated before installing the mod.

⚠️ Be careful: this process is resource-intensive. It recalculates every air block in the chunk and updates all surrounding water, triggering physics and neighbor updates.
When used with mods like Particular (that add 3D splash particles), it may cause lag spikes or even crashes.

The command finishes after flooding nearby chunks — you can run it again to continue.

(1.21.5+) /inundated vision on/off — off by default. Gives the effect of night vision when the player's head is in the water. If the player swims out, the effect is removed.

KNOWN ISSUES

1. Generation of any new chunks is now many times slower than in vanilla.
2. Updating large lava lakes in the nether will probably cause a lag spike.
3. The End is flooded at a lower level of generation, causing the world to disappear chorus; end crystals have pockets of air; the portal generates on Y 320, therefore, the dragon's egg is unattainable; end cities are barely flooded.

COMPATIBILITY

Mods that change vanilla generaton or dimensions should work fine, since the flooding of the world with water occurs at the very end.

New dimensions will be filled in depending on whether the populateEntities method is used there or not.

CREDITS

Almost all the code is written by ChatGPT, I just used my promt engineering skills, logic bulding and inundated with solving a bunch of errors, the solution to which I had to look for myself in yarn mappings.
I'm surprised it works at all, but I really wanted to make this mod and make it open source, since its alternatives are behind a paywall - GPL-3.0 now.