[Legate of Amon Lanc]

Very nice post, and welcome to the 'Downs, Feliandreka. I like the idea of Ulmo trying to help the Children still, however there are some things in your post which I would dare to oppose.

Originally Posted by Feliandreka

Ulmo has power in all waters, again from several references in Silmarilion, and therefore was most likely present at the Gladden Fields where the Ring betrayed Isildur. Being a major magical item (forgive the D&D sounding description of the Ring) which was host to a large portion of Sauron's power, it seems reasonable to me that Ulmo the Valar or one of his Miar minions may have known about it simply by its being in a finger of his domain, Anduin the Great.

Here is another leap of conjecture based on my own faith in Ulmo and his lasting concern for the Children. He knew where Gollum had taken the Ring by virtue of being connected to the underground lake Gollum called home "at the very foundations of the Earth" (there it is again, another reference to Ulmo's power from the Silmarilion) that lake is connected by waterways to Anduin the Great and the Sea. At the time there is no defilement in the Misty Mountains to keep Ulmo out as Morgoth and Sauron were able to do. Goblins have no such power. The only creature capable of that might have been the Balrog but he was many miles to the south in the Mines of Moria.

The point is, I think Ulmo did not have any power anymore over all the waters in Middle-Earth, as he didn't have in Beleriand a long time ago. All I say here is just my belief, but I think that it was not about particular rule in the sense that the waters in the lands ruled by Morgoth or Sauron would be spoiled and the rest would be okay and clear from his influence. I believe the "essence of evil" was spreading simply by the time as it went, because I got the impression from the books that when it comes to things being spoiled, with Arda (Arda Marred!) it goes from good to the worse. Beleriand was slowly "overrun" by Morgoth and Ulmo could no longer use the waters to their "full potential", so to say. Ulmo tells Tuor:

Originally Posted by UT

and the shadow of the Enemy lengthens; and I am diminished, until in Middle-earth I am become now no more than a secret whisper. The waters that run westward wither, and their springs are poisoned, and my power withdraws from the land; for Elves and Men grow blind and deaf to me because of the might of Melkor.

I believe this does not apply only to this era, i.e. that by the War of Wrath and defeat of Morgoth this effect is not annuled. First, Beleriand of course drowns. Second, after the Drowning of Númenor the Valar lay down their reign over Arda. So technically, even then if Ulmo still HAD any power over the waters in M-E, he should NOT have it anymore after that. However, here I would accept, and maybe even encourage, the possibility that Ulmo would not simply leave it like that. Being the "voice that gainsayeth", he could have as well kind of trespassed this, even further than the Valar just sending the Istari to Middle-Earth (besides, Ulmo did not send any of "his" Maiar with the Wizards - interestingly, as he cared for M-E - so the logical explanation could be that he was engaged with M-E already in some other way, and possibly even on a deeper level).
Nevertheless, I believe, as it usually goes in M-E, that what had already been marred by Morgoth in the First Age was NOT undone, and maybe it even continued, and Men and Elves remained "blind and deaf", in their basis, or then, when Sauron emerged, they again grew "blind and deaf". And as Sauron's power grew, I would say that it's been the same as with Morgoth: Ulmo's power, if there was any still, was withdrawing from the land, too. And that was despite whether Sauron's power was or was not currently growing. It was sufficient that he still existed. Remember Mirkwood: even after Sauron left it, it remained a dark place (and he really left it, for some time, totally).

I am not saying that the waters were totally marred. I think actually, water by itself, "on the very molecular structure", so to speak, was "unmarrable" and had something good in itself (it echoed the Music the best of all things); so for example the Nazgul could not cross the water, whether there would have been Ulmo's direct power right now or not. But I believe if he wanted to interfere directly, he would have to at minimum face many obstacles, and for getting information from the waters in M-E, he certainly got a lot of "interference".

A side note: Have you noticed something interesting in this text I quoted? Ulmo refers to Morgoth as - Melkor! That's actually nice. Everybody started to call him Morgoth in Middle-Earth, and probably had you asked me what Ulmo calls him, without looking into the text, I'd say Morgoth, if for nothing then perhaps just because the people in Middle-Earth are used to it. Interesting, huh? I think after all, Ulmo thinks of Morgoth as "Melkor" - okay, he was used to it, but still - for Tuor it must have been quite shocking to hear "Melkor". I can't think of a good example from our world, but just imagine let's say a band of rebels from the Star Wars, and suddenly one of them would start refer to Darth Vader as "Anakin". That'd be weird, eh?

But back to the topic. That said, even if you contradicted this and said the Great River was at least as large a flow that actually the power of Ulmo could not have disappeared completely from there, I would disagree about the underground lake. I don't think this lake was in any way directly connected to Anduin: after all, it was an underground lake. And for some reason, I think that Ulmo's power did not reach much deep into these waters which were not connected directly, i.e. through flowing, not ground water to the Seas etc. Nasty slimy things, lost pools in the heart of mountains: depending on the circumstances, I think some of those may have been nice and clear places with the "primal" unspoiled water, but as the Ages went by, they became "contaminated". In any case, Ulmo's access to the underground lake would have been far more problematic than let's say to the Bay of Belfalas, from the merely "materialistic" point of view.