Rey-Goor, the Black Bayou is a location on Mirrodin. The Scars of Mirrodin Style Guide describes it as follows:
|| The forests extending from the Tangle to the Mephidross gradually become more oil-soaked and gloomy until the ground sloughs away into a stinking bog. The twisted and dying trees send metal root-spikes above the black water and act like islands of solid ground in the sucking vastness of the bayou.
The creatures of Rey-Goor weren't exempt from Phyrexianization, as shown by Putrefax.