A não oficial " página inicial do Pirates of Dark Water" tem isso a oferecer sobre o assunto;
From the entire series, seen first in episode 3, "Break-Up." The true antagonist of the series. This "deathly liquid" is manufactured in the center of Mer (by the Dark Dweller, I believe), but was held at bay for eons by a magical seal produced by the Thirteen Treasures of Rule.
After the Dark Dweller causes a rift in the ocean bed and in the Treasures' seal, the Dark Water emerges in the seas of Mer, starting the Year of the Black Tide. It engulfs anything in its way--ships, debris, people, you name it. It also destroys nature--Andorus was ravaged by the Dark Water, and Octopon was as well, though more so by Morpho and his Dark Disciples--Bloth had actually plundered the city and left it in ruin.
The purpose of the entire series is to show Ren's quest to retrieve all Thirteen Treasures of Rule and bring them home to Octopon so he can place them in the lighthouse, which is the location of the new Seal (or so it seems), to seal the Dark Water back into the planet's core and to stop it from ravaging Mer.
If the Dark Water wins, or if Ren and his friends lose (to the Dark Water or to Bloth, or to some other malignant force we don't know about)--the world is doomed to be literally engulfed by Dark Water, and every bit of life in every corner of Mer will be destroyed by the semi-sentient liquid.
Parece que nas ocasiões em que você pode ver um rosto na Água Negra, você está realmente vendo o rosto do Morador das Trevas.