Origin of the Oceans

While arguably the largest body of water on any of the planes, the vast oceans are said to not be connected with the elemental prime of water. Old archives mention the four prime elements: Earth, Fire, Air and Water, but written texts about the elemental prime of water only describe fresh water: Lakes, rivers, rain and clouds. So where did the oceans come from? Among scolars of planar studies, it is relatively common knowledge that the oceans have always been there, and that they are likely the surface layer of the domain of Chaos. Chaos existed first, and so the ocean, they argue, must have existed as well, even before the four elemental primes formed, which in turn imposed order on Chaos and thus formed the natural planes.
The focal point of the oceans seems to be somewhere in the Underdark, a body of salt water called The Dreadlake, that connects all the oceans and which is said to be the resting place of all the ships, as well as their crew, that sink in open water. It is a place of high Similarity, making it a place where planar crossings appear frequently, which strengthens this hypothesis.
There is but one source for the myth surrounding the Dreadlake, an inscription in stone, unearthed long ago but in a language not native to the plane. The fact that the source is written in the language of Chaos - which in itself is a rare sight - lends credibility to the story, however, due to the nature of the Chaos language, the exact meaning cannot be ascertained. The translation commonly accepted by linguists to be reasonably close to the expected meaning of the script can still be found in many books concerning origin mythos and planar lore. Only an excerpt is given on the right, as the complete text is somewhat lenghty and many parts are still shrouded in controversy. This part is one that has a high level of consensus, however.
An eyewitness told that they once saw a broken ship slowly rise keel-first from the surface of the lake, upward until only the tip of the mast touched the water, then came crashing down and sunk into the deep blackness of the Dreadlake, and the echoing sound of a bell struck twice welcomed the bloated crew to their final resting place. Another eyewitness spoke of a place in the Feydark, at the same geographical location of the Dreadlake in the Underdark. It looked like a bottomless black pit, with large, serpentlike creatures far down in the depths. The sound of a bell struck twice, and one of the serpents came swimming up through the void. The witness then fled. Scholars say this could prove that the oceans are connected to the Abyss, the second layer of Chaos. Others are sceptical, however.

From where they went to where they not aspired to arrive. An origin, and end. All the same, never equal. Their eternal slumber ends, a voyage through their waking starts, then abrubtly ends and they sink back into slumber once again, once again sink back to where they once awoke. All arrive here that end, a lake of dread and of salt, and of sleep and of slumber, and of deep and of darkness too.

— Excerpt from the myth, translated to common