On the ecology of Onnen’s waters:
Although most of Onnen’s coastal inhabitants are accustomed to the midnight color of our oceans having grown up with them that way, this hue is actually an unnatural one when viewed from the perspective of an outsider. Beyond what we can see from shore, there is actually a shelf in the Shilluk Ocean where the seabed rises up and divides our homeland’s waters from all those surrounding it. You can think of it as a barrier similar to a wall, except you cannot see this wall jutting out of the waves like the jagged rocks you might imagine. This continental shelf is not like that, but its barrier is very noticeable.
At the border of the Shilluk Shelf, the midnight blue of our oceans clashes in a definitive line with the lighter blue of the outside world’s oceans. In testing these banks, we have discovered that the source of our water’s hue is, in fact, a species of algae that only inhabitants the waters within our protective barrier. This algae helps keep our waters separate and is a vital part of the diet for our native fish. It is found in all large bodies of water across Onnen, including the Tuareg and Acholi seas, with its greatest populations existing in the Shilluk Ocean proper.