Weird square of water in caves

i was playing on a realm with my friend when we went into a cave and found a weird square of water i thought an admin just put it there but then on my own world i found the same square of water the seed is 8481418460515074592 the steps that i used to make the image was that i input the seed "8481418460515074592" and then teleported to "230 -40 430" and i was then in the cave with the square of water and took another screenshot of it.