It happens in Alik'r desert, Craglorn etc. When approached, these pools can appear solid black. Turning around yourself makes this problem briefly disappear. I can also see water reflection flashing and distorting, followed by black color, so maybe there's problem with the reflection of the surroundings (because when reflection is visible, there's no blackness).
It happens exclusively on these pools and this problem persisted at least 1 year.