Chaos Well

The Chaos Well was a corrupted fountain that was created by Mannoroth.

Background
When the Burning Legion went to Kalimdor after destroying Lordaeron, Mannoroth and Tichondrius went to a glade in Ashenvale to consider using the orcs to defeat Cenarius. On Tichondrius' suggestion, Mannoroth proceeded to spill his burning blood into a Fountain of Life, corrupting it, and causing anyone who drinks of it to be infused with the Blood of Mannoroth. When Cenarius attacked the orcs, Grom Hellscream took a detachment to explore the forest. Grom and his band found the Chaos Well and drank from it, reinvigorating the blood pact between them and Mannoroth and becoming chaos orcs. The orcs proceeded to use their new found power to kill Cenarius, and the night elves that were defending him.

In World of Warcraft
In World of Warcraft, the Chaos Well is no where to be found.

Much of Ashenvale is not very open, and is not very similar to the Warcraft III version of Ashenvale. It may have not been included for scale reasons.

The Chaos Well might have depleted itself and crumbled (if this is even possible), or the local satyrs and demons could somehow be related (somehow).

Although also not proven to be true, there is some evidence that supports that there may be more corrupted or chaos wells found in the Barrow Dens since there are corrupted creatures located there.