So i created a world and started to build lets call it a base inside a mountain and the mountain is right beside a deep ocean biome and when i opened the world to finish my "base" i found a massive hole in the ocean which wasnt there previously. Is there anyway to fix it(im trying to avoid placing a layer of dirt and putting water ontop but ill do it if its the only way). Any suggestions one how i can fix it?
If you play this on the PC, remember to ALWAYS back-up your world after each save and also back it up to another device. There's no point backing it up to your internal hard drive just encase you get a major PC crash. If Minecraft or your PC crashes up you'll always have your world backed-up in a flash drive or an external hard drive and then you can copy and paste your world back in and resume as if nothing went wrong.
Yeah looks like some kind of chunk error/corruption which could be caused by any number of things. If you haven't built anything in that area, just use MC Edit to delete those chunks and let them regenerate. If you don't know how to do that, try posting here