These are new will be added on update, they are added much as they can world wide if working from Bing see this thread Water Masking.. It's just so Beautiful!
They are all in the sim from Bing, but by default are underwater, you don’t see them, they are updating these manually in the sim to get in higher visible level when those Bing imagery are ok and no real glitch, the masking became visible with editing.
If they would be enabled these all at once, you would see many glitch and layers, would be pretty odd to see, now as usual you would see meh post like “too many tiles shallow awful masking tiles” please fix them.