Ush

Elemental Plane of Water

It is an ocean without a surface.
It is domain of current and wave.
It is a bottomless depth.

- Manual of Planes

Planar Movement

Ush has a planar period of 256 days and a terminal period of 12 days, 19 hours, and 16 minutes. Ush primarily affects Nemas through the ebb and flow of water, causing weather and tidal fluctuations. Ush's coterminous time creates a monsoon season, conversely its aterminous time is extremely arid and causes part of the plane to become desert-like.
During its coterminous period, Nemas experiences frequent rainstorms and the ocean level can rise as much as 15 feet. As per every elemental plane, elevated power of related magics and an increase in associated elemental creature sightings occur during the coterminous period. The increased power of magics does not manifest in everyday spellcasting. It increases the amount of water and cold energy in the plane and allows for a ritual to channel more than the usual amount. For example, the Ulsce Family uses the coterminous time to replenish the water stores in the city.
During Ush's aterminous period, Nemas experiences major droughts. The barren plains become cracked and the Fabled Rise lose their snowy tops. Fortunately, Lonnhaven's barrier protects it from the effect. Opposite of the coterminous state, the aterminous state sees a decrease in related elemental magics and associated creatures of Ush are infrequently seen.

Geography

There was no deep or shallow, no dark depths nor wavy surface, just an endless ocean that felt as if you were submerged several feet (say a couple meters) in any body of water on the Prime Material Plane. There was no sun, yet the water itself seemed to glow dimly with a bluish green luminescence. Volumes of water at any temperature and salinity could be found if you knew where to look or had a guide. This plane had all varieties of water constantly in motion, influenced by currents and tides. Life that depended on particular conditions flowed along with their preferred environment or suffered the consequences. Impurities such as bubbles of air, chunks of earth, and even short-lived balls of fire could be found floating about due to elemental vortices or the workings of powerful beings. Habitats and settlements typically formed near sources of food and shelter, or near portals and vortices to facilitate trade.
Supporting the teeming life of this plane were the corals and plants that made their way here and found purchase. Huge drifting three-dimensional reefs and loose spheres of freshwater grasses, kelp, and seaweed were home to myriad species and were fertile fishing spots. Travelers had to keep in mind that large predators knew of these fishing grounds also, or else they might discover just how bite-sized they actually were. Just like a Prime ocean, the Elemental Plane of Water seemed to have no limit on how large some creatures could be as giant squid, aboleth, and kraken were known to prowl the plane. Small creatures could be deadly too, with poisonous spines or barbed tails. The smallest of them all was perhaps the deadliest: algae that formed the infamous "red tide". Exposure of the eyes or lungs to the red tide caused a blinding sickness as virulent as any disease.
If the Plane of Water had any weather, it was the currents, whirlpools, tidal bores, and flows of ice, steam, or silt that could inconvenience a traveler or be a deadly surprise. Usually invisible, currents could be strong enough to pull visitors off in some direction for long distances before they were able to exit the current. Tidal bores were the most dangerous currents, hitting like a thrown boulder and carrying the unlucky creature away for miles (kilometers). Whirlpools were caused by countervailing currents that sucked everything in a tightening spiral, some of which lead to vortices to other planes. Ice and silt flows were fairly easy to spot before encountering, but steam flows were nearly undetectable and could cause nasty burns or boil the flesh from your bones.

Fauna & Flora

It is difficult to determine what type of creatures were the most numerous in the Elemental Plane of Water but presumably the water elementals had the upper hand because they were manifestations of the plane itself. They could take on any shape their fluid bodies could form but they were extremely hard to see and therefore were often described as blurry versions of Prime Material Plane animals and monsters typically of the aquatic variety. Water weirds, an intelligent life form that could possess water elementals, were also thought to be native to this plane.
All other peoples and creatures are interlopers or inadvertent immigrants by way of being sucked through an elemental vortex. Those that made a home here and thrived included the marids, the nereids (aquatic fey), and the tritons. Besides almost every species of salt- and fresh-water marine life, there were reports of sightings or encounters with many creatures including aboleth, black and bronze dragons, mephits of the ice, ooze, steam, and water varieties, sea hags, and will-o'-wisps.
Trade also brought many different races to the Elemental Plane of Water. Merchants that traded with the dao and the marids included aquatic elves, humans, kuo-toans, lizardfolk, and sahuagin.

References

Elemental Plane of Water | forgottenrealms.wikia : A majority of content relating to Flora and Fauna and Geography was gathered from this location.

Type

Dimensional plane