Badges update automatically and link to the data pack page on MineUniverse.
Full credits to dannytaylor, who created the datapack, and to judgealexander for the original idea.
The photos show it alongside mods from the list; the datapack on its own does not generate any kind of island or any non vanilla structures.
Minecraft's biomes are not removed or replaced: all of them, including the ones that would normally be terrestrial — such as plains, forests, desert, or jungle — still generate, just submerged now. This means structures associated with those biomes (villages, temples, pyramids, mansions, or ones from mods/other datapacks) also keep generating normally.
In addition, the seafloor of non-oceanic vanilla biomes is lightly enriched with underwater vegetation.
This datapack has only been tested on NeoForge.
It doesn't depend on any mod, but the following are strongly recommended for a better experience:
MAIN
It's designed to coexist with mods that add their own marine or terrestrial biomes and/or structures (tested with everything on the list above, and with many structure mods as well): since the datapack doesn't replace or block the Overworld's biome list, those mods can keep inserting their biomes and structures normally, without conflicts.
Notes
Version for 1.20.1:
I only changed a single number inside the datapack to make it compatible with Minecraft 1.20.1. To visit the original creator, click here.
I recommend using it together with structure and biome mods, since some of these will generate around the world, filling it with life instead of just an empty ocean.