Water reflecting abyss?

[Acies]

That got rid of the trailing, but it still leaves a weird box in the water that immediately vanishes once I get close to it.

Spoiler below!

Edit: I just changed the water texture from Morgue to ArchiveCellar and it looks fine now. I guess the Morgue water texture is just borked somehow. Thanks

It can have to do with cubemaps and texture size on the plane - you could try creating a copy of that water material, but without a cubemap.