Inundated

The mod floods existing worlds with water, and newly generated chunks are filled as well, which makes chunk generation many times slower than vanilla. Air cave blocks are replaced with water, and blocks that can be waterlogged, such as leaves, slabs and fences, are waterlogged so they stay visually consistent underwater. Torches, sugarcane and nether vegetation are removed when they would be flooded, and dropped items are affected the same way. Large lava lakes can cause lag spikes when they update, because they are replaced by water as well.

Inundated turns the game into a survival challenge in which the player must adapt to living entirely underwater, figuring out how to explore, build and gather while submerged. A command floods nearby chunks and stops once it finishes, and it can be run again to continue. Whether the populateEntities method is used decides how the new dimensions are filled with water.

Players join without it, since only the server has to run the mod. Fabric API is required, and files are published for Fabric alone across 1.21.4 – 1.21.8. The code is open source under the GNU General Public License v3.0 or later, and source code and an issue tracker are linked publicly.