In centre of the tombs and wastes of Imlad Balchorth lies an isle surrounding by green, vile water. Starting here and north-westward the fell waters do not simply addle the mind, but entirely overcome those who touch it.
It is on this isle that the "Gaunt-lord of Pestilence", Ferndúr the Virulent, is said to lie. Among many fell-spirits and shades, this isle is no doubt the most dangerous part of the already dangerous area. Ferndúr doesn't simply show himself for anyone; and it would likely take a large disturbance to Gurthlin to raise his ire.
These creatures are encountered at this location: