I noticed that in my game, the borders of the land and the water are really bad in quality. Also, if i stand near a river, i can see straight lines, which are the borders of the water. It looks almost like glass. Is it normal ingame? I am using realistic water texture (RWT).

I'm on PS3 and the only 'seams' I've noticed are in the icy caves and it's not too bad - only a few.

The only weird thing I've noticed about water is that some areas seem to have invisible pockets. In some areas you'll fall a few feet and then do the deep breath/gasp for air like you've surfaced even though you're clearly (read murkily) underwater.

On Xbox I get the effect where the water becomes like a glass table top as well. Then as you move along you get to a point where it's part blue and part glass table. Move some more and it goes back to normal. Not a big deal and was actually helpful once because it allowed me to see a chest I would have never found. Not that the chest was anything great. Something like an iron sword and 21 gold. Off topic a bit but the underwater chests are spectacularly unspectacular.

I don't use any mods for landscape, water, FX, etc. I find most of the game just fine on "vanilla" settings - GeForce GTX 460 SE, and both WoW and Skyrim, not to mention Oblivion, run fine on ultra settings.