I upgraded to 1.13 from 1.12 and moved to another location on the map where I thought I could locate turtles. I came across a wall of tall kelp and then found an unusual matter that seems very much like a bug many others reported in the past and was fixed. This world had not been upgraded from 1.12 to any snapshot of 1.13.

In this case, random water or air columns appeared much like in MC-129625 and there is no coral to be found. Another strange occurrence was that there were multiple turtles in the area when I found it, however they will not return to this area. Additionally, when it becomes dark, these air columns give off light and mobs will spawn here but not enter the water. They will however, randomly appear on top of the water above these areas.

I was able to swim down and lure several zombies into eventually entering water and becoming Drowned, however they carry nothing at all times.

What I expected to happen was...:
I expected an object to be where the air columns are, either corals or sea grass.

What actually happened was...:
There was partially lowered ocean, where large areas of these columns glow at night and mobs spawn but without any items.

Steps to Reproduce:
Enter seed or load world and jump to my area. Examine the unusual water below.