Zangarmarsh is a hauntingly beautiful swamp covered with a forest of giant mushrooms. Though largely teeming with life, sections of the swamp have begun to die of late, and the sapient fungi of the region seek help in returning it to life. This zone is located in Outland to the west of Hellfire Peninsula.
Worldofwarcraft.com says the following about the Zangarmarsh:
Zangarmarsh is a tranquil area that has largely evaded the demonic influence. The marsh's innumerable lakes and pools are clean of any taint, and most native animals and fungi give off soothing phosphorescent light. Only recently has the area's self-contained ecology faltered. Something is causing the water levels to drop. The marsh's giant mushrooms are dying, as are the creatures that rely upon the mushrooms for food.
Not very much is known about the past history of Zangarmarsh as it was not mentioned in Warcraft II. It does not even appear on the map of Draenor. In Rise of the Horde, it is described as the place where Velen and his surviving followers hid after the orcish genocide and waited until their raid on the Exodar; it was also where Akama led his own followers in the trailer to Patch 2.1.
With Illidan's Naga draining the waters and the Ango'rosh tribe cutting off the mushrooms for their own needs the ecology of the marsh is being severly affected, if the Cenarion Expedition doesn't act quickly the marsh could be destroyed.[1]
Zangarmarsh consists of a large expanse of swamp land, bordered by mountains to the north, south, and to some extent the east. A long stretch of coastline forms the western edge of the zone. Giant mushrooms are the characteristic feature of the area, towering above the pools of marsh water like great trees.
Zangarmarsh contains four instances all located in the Coilfang Reservoir, one of which is a 25-man raid. This area has no battlegrounds or micro dungeons, but has a world PvP zone for a graveyard nearest to the Coilfang Reservoir entry.
(Note: as of Feb 03 2008, at least for Alliance, the graveyard only works for the Slave Pens instance as the distance to instance portals is used instead of the distance to the Coilfang entry).