Minecraft wiki entry for Updating_old_terrain, associated text: An example for a non-breaking update is Java Edition 1.13. This version vastly changes the world generation of oceans, swamps and rivers by adding features like shipwrecks, coral reefs, and seagrass. However, the new terrain generation doesn't affect the biome type or terrain altitude (with a few exceptions, as u/bdm68 pointed out.)[1]