[The Might]

...you throw a Ringwraith right in the middle of the Sea?
I mean, they are invisible when unclad, but not in the way that matter can go through them, so they would probably sink...since I doubt they can swim judging by their fear of water
But they can't drown either, as seen after the huge flood of the Bruinen when they quickly returned to Mordor
So...would they lie around on the bottom of the Sea, or would they run around on the bottom of the Sea? I dunno, maybe you can help me out with this one