Places where some caves intersect with water biomes such as rivers or oceans will generate a thin wall following the contour of the water, separating the water from the cave, resulting in the water often overhanging the cave separated by only a 1-2 block thick layer of dirt or stone.
Sometimes the cave will generate a 'bubble' in the water biome, surrounded by similar thin walls.
Steps to reproduce:
Generate new world using seed: 4675047371479781160
Go to coordinates in attached screenshots
Attachments
Comments 2
Sometimes these aquifiers look a bit weird but the walls are there intentionally to prevent the water from flooding these caves entirely - but occasionally these walls have holes in them to create waterfalls!
See also the Minecraft Wiki article on Aquifers: https://minecraft.fandom.com/wiki/Cave#Aquifer
The only bug that I see within this report is within the
attachment, and that problem is MC-248531. As for the other images, these are just aquifers which are an intentional terrain generation feature. Aquifers vary in shape and size a lot and can cause rather interesting generation.