A pool of foetid water is in the ancient city within the Paths of the Dead.
'The Morthond, the great river that flows through these lands, begins from within the Paths of the Dead. Rumour is Lenn Dûskud, a pond within the ancient city, has been corrupted by the dead within. If those waters were to find their way into the Morthrond the entirety of this region would be irrevocably harmed.
'Venture north to the Paths of the Dead, find this city and remove any ruthless rune-stones within this pond that could corrupt the waters.'
Lenn Dûskud, a small pond, is at Kêr Izel, within the Paths of the Dead, far to the north of Dol Amroth.
Golusel asked you to venture to a pond within the Paths of the Dead and clear it of any foul objects.
Golusel is in Dol Amroth.
Golusel will be pleased to hear the waters have been cleansed.