LoTRO Lord of the Rings Online Dark Water
From out of tranquil rivers and soothing lakes rise the corruption, Dark Water. Also known as Mornen to the elves, these vile spirits composed of bone, and black liquid. Existing only to destroy the Free Peoples of Middle-earth, Dark Water will never ease their assault, they will never flee for fear. Once they have begun an attack, they will kill or be killed with equal satisfaction.
Another invention of Turbine, rather than Tolkien, Dark Water expands upon precedent set by the wights of the Great Barrows. The expanding Society of Evil Spirits might just be the biggest guild in Middle Earth if only they could organize.