The Pelagic

Overview

An excerpt from the notes of Dr. Jarvit Dykane, scholar and explorer based in Jalekhar
At first glance, the Pelagic appears to be as plain as can be: an endless expanse of still water, illuminated only by faint twinkling stars (or some facsimile of them) far above. Though it was one of the first elemental planes to be discovered, exploration had to be postponed until researchers could develop a way to transport not only a few people across planes, but an entire ship that could propel without the use of wind and sails. (Curiously, this also led to the breakthrough discovery that nonsentient objects have a different relationship with the planes compared to sentient beings, as the implications of that relationship.)
Initial expeditions were short and simple: testing the composition of the water and the ability to breathe using conventional spells; collecting fauna and experimenting on them (or attempting to eat them plotting one's location over several visits using the false-stars above. With the invention of fire-fueled propulsion (and planar shifts large enough to fit such vehicles) researchers were able to propel further, spending extending time along its lifeless seas... until one day, in 734 N.M., they came across their first island.
It was a small thing, comparable in size to Isle Santoris off the coast of Lucresci. But on a particularly fog-less day with no apparent horizon in sight, their lantern lights were easily visible as the ship approached. There was a small tribe there, not more than 200 in size, but fairly well sustained nonetheless. Despite seeming fairly human in look and anatomy, they were all extraordinarily well-accustomed to darkness and to traversing the waters without cold protection. Much of the plant life was adapted to thrive in low-light conditions or were even bioluminescent -- scientists are still trying to determine their primary food source, to little avail. Though there were a few small land animals, mainly avians, most of their meat came from aquatic creatures, fish and amphibians and what have you. They constantly kept a small beacon lit up in the middle of the island, slightly above the treeline, fueled by a mix of bioluminescent mushrooms and fish bone kindling. ( Taking some of these fish back, it was confirmed that cooking them with the bones still intact gave off the scent of burnt charcoal and ashwood. )
Despite their seemingly primitive surroundings the expedition noticed that they had scrapes and salvages of rather advanced technologies -- spears tipped with scrap metal, ceremonial headdresses of fine silk, even reams of paper and a few bottles of ink, used conservatively to preserve knowledge from one generation to the next. When asked about their sources they said that sometimes things like that simply washed up on shore, but for the most part they traded with other islands... when they came around.
Though it was difficult to prove, over the span of a few decades it was indeed confirmed that these islands, not bound to the rules of plate tectonics or currents or anything of that sort, appeared to randomly and significantly drift throughout this endless expanse of sea, After however long (they don't really keep track of time here) these various tribes came up with the idea of keeping bright beacons lit at all times, so that when one was seen through the fog a trading vessel could be rowed over for a loose sense of commerce. While many were simple like the mushroom tribe, there have been reports of larger landmasses, up to the size of Josefa, with cities and villages rivaling those of early pioneers to Izera. Though much rarer, explorers have even caught sight of such wonders as entire communities living off of a collection of boats tied together, and a wandering seaperson (referred to as a "triton") coming not across the ocean but from below it, from some underwater civilization. ( Not to say that the other islands aren't wonders -- everything becomes strange when the laws of the material plane no longer apply.)
No one knows for sure how these people came to live here in the first place. It has been speculated that this is where people disappear to when they're swept to the bottom of the ocean, or overtaken by a harsh, disastrous tsunami and there's no sign of their disappearance. This phenomenon, which some scholars have taken to calling a "seam", is by its nature difficult to find evidence for -- though, remnants of what appear to be lost civilizations have turned up during various extended expeditions into the plane. In any case, it is nearly impossible to conclusively match up islands to material world equivalents; without a day and night cycle, time in this plane has appeared to ebb and flow -- albeit, to a seemingly much milder scale now that expeditions into the watery unknown are more frequent.
Though some more adventurous factions of the Cartographer's Guild have expressed an interest in venturing underneath the waters, the research is far from making that a reality. One would need a vessel capable of illumination, self-propulsion, capacity for breathable air... the requirements are endless, and cutting corners in such a dangerous landscape is the equivalent of a death wish.
And yes, it can be inferred from tribal legends, and the ecosystems, and the large bones that constantly run ashore that the Plane of Water is just as dangerous as every other plane where anything can happen.
Speculations have been made of a possible connection with the terrapin-inhabited Siwa Isles, in the middle of the Cremir Ocean, but lack of academic influence on this region has made such research difficult to make headway in.