The legend goes:
In a place all dark and dreary.
A well so noxious, the eyes get teary.
With bubbling muck and oozing goo.
A choking gas will mean the end of you.
Filled with the souls of the not-so-dead,
This pool claims all, who dare to tread.
Orcs and man, they both will die there.
For Sauron's Pool is the living nightmare.

***

Well, he had to make it scary, or else others would come over and use the pool.

Apologies to J.R.R. Tolkien