formed from reading this part of the Anuad Paraphrased:
A large fragment of the Ehlnofey world landed on Nirn relatively intact, and the Ehlnofey living there were the ancestors of the Mer. These Ehlnofey fortified their borders from the chaos outside, hid their pocket of calm, and attempted to live on as before. Other Ehlnofey arrived on Nirn scattered amid the confused jumble of the shattered worlds, wandering and finding each other over the years. Eventually, the wandering Ehlnofey found the hidden land of Old Ehlnofey, and were amazed and joyful to find their kin living amid the splendor of ages past. The wandering Ehlnofey expected to be welcomed into the peaceful realm, but the Old Ehlnofey looked on them as degenerates fallen from their former glory. For whatever reason, war broke out, and raged across the whole of Nirn. The Old Ehlnofey retained their ancient power and knowledge, but the Wanderers were more numerous, toughened by their long struggle to survive on Nirn. This war reshaped the face of Nirn, sinking much of the land beneath new oceans and leaving the lands as we know them: Tamriel, Akavir, Atmora, and Yokuda. The Old Ehlnofey realm, although ruined, became Tamriel. The remnants of the Wanderers were left divided on the other three continents.
Almeris (Old Ehlnofey) was a world that had oceans and seas, it was also a world that had been protected from the chaos of Nirn when it was first created, safely hidden until the other Ehlnofey (the Wanderers) came upon it.
When the war broke out between Old Ehlnofey and the other Ehlnofey ( the Wanderers) in which the Wanderers were the victors, Almeris bubble was broken and its seas and oceans were released into the lands of Nirn.
are there any known in the lore of them? or speculations? Like Y'ffre perhaps being a god/spirit of the land/forests.
Nereids are the first things to come to mind; Shada and her daughters had worshipers, and we get spirits/memory echos/whatever of a Bosmer tribe in Greenshade who worshipped a different set.
Beyond that Umaril the Unfeathered claimed a god of a "World River" from the previous edition of the world was his father. I don't know if said father was a Nereid also or something else; the in-game model for Nereids is female but it doesn't necessarily follow that they all are. On the flip side, it doesn't necessarily follow that they aren't all female either, I don't believe the topic is particularly well-documented in the game lore. But at the very least you've got one type of water spirit floating around.
King Orgnum might count:) though to me he seems more like a Master of the Seas - not truly a God of them. Of the et'Ada Kynareth did seem the closest to me as well, until I came across lore of a Magna Ge named Xero Lyg and a continent with nineteen nine and nine Oceans that were once enslaved and then set free? also something of a 2nd void. So I wonder of this now.
Was a second space created in the void by this Magna Ge? that had oceans? at the same time Kynareth might have created this space for the creation of Nirn?
These are little bits of what I have read that brought these questions to mind.
Kynareth (Goddess of Air): Kynareth is a member of the Nine Divines, the strongest of the Sky spirits. In some legends, she is the first to agree to Lorkhan's plan to invent the mortal plane, and provides the space for its creation in the void. She is also associated with rain, a phenomenon said not to occur before the removal of Lorkhan's divine spark.
The Void (also called the Darkness) is the name applied to the dimensions outside of the known realms (e.g. Aetherius, Oblivion, and Mundus) of the Aurbis. It is also occasionally used in a more limited capacity to refer directly to Oblivion. The brothers Anu and Padomay came from the Void, as well as Sithis, who originally caused change in the world. . Legends say that deities wishing to create a new plane of existence must initially create a space for it in the Void. The "Second Void" and the "Nineteen Voids" are unknown terms which may be related to this dimension.[OOG 1]
According to the teachings of Mankar Camoran, Lyg was the name of a continent that existed when Nirn was ruled by the dreugh in the Dawn Era.
The tyrannical dreugh-kings enslaved the "nineteen and nine and nine" oceans of Lyg and fought constant border wars among themselves. This correlates with the teachings of the Tribunal Temple, which state that Molag Bal had served as the chief of the dreughs in a form that was "spiny and armored and made for the sea", the after-image of which was reborn in Tamriel and known as the Ruddy Man.
"On the world of Nirn, all was chaos. The only survivors of the twelve worlds of Creation were the Ehlnofey and the Hist. The Ehlnofey are the ancestors of Mer and Men. The Hist are the trees of Argonia. Nirn originally was all land, interspersed with seas, but no oceans".
that Nirn originally was all land, interspersed with seas but no oceans.
So the Seas would have come from the Ehlnofey world, though not the Oceans?