The Plane is populated by elemental water spirits, that know nothing but the constant ebb and flow of the ocean currents. Through exertion of their will they can move about the plane and create currents of their own. As the eons pass these beings' wills become stronger, and they are able to control more currents. Also as their existence is simple they often engage in contests of mettle; when these (rarely) end in death the victor absorbs the essence of the loser to grow stronger still. The plane is also home to the Marids, a race of genie that is as fickle and transitory as the waves. They live mostly near the Plane of Earth, where there is solid matter that they can shape to their purposes. They have many small cities there. Their independence prohibits strong government, but they can briefly unite under a strong leader under times of invasion. They often command the elementals as servents and soldiers.
Near the border of the Plane of Air the seas stop. Closer to the Positive Plane great rolling waves can be found, and great mists and fogs. More toward the Negative Plane the air and water grow colder, until great towering mountains of ice can be found. Eventually the entire surface of the sea is frozen miles thick. As we approach the border with Earth we find small floating islands*, buoyed by their attraction to their home plane, but held back by currents of water. Gradually the islands grow larger, until we come to a limitless expanse of coastline. This muck, where water has seeped into the constituent earth, is miles thick. * Note there is no air, so the islands are really blobs of earth in the endless sea.
The Plane of Water is a vast ocean, greater than any seen on the Material Plane. It's murky depths go on in every direction for countless miles. The salinity increases towards the border with the Negative Energy Plane, and decreases towards the Positive. The seas are brighter towards the Positive as well.