Hello! I have had this issue for a while, and I was hoping it would get sorted in a patch, but it is still there.
I have tried to google the issue but I can't seem to find a solution.
The game was working fine for about two weeks, then when I got to Skelige all the textures just became low res.
I have a GTX 770, AMD six core 3.8ghz and I'm runing the game from an SSD. I'm on W7 64bit.

Thanks for reading!

Have you installed any patch recently? The patches used to reset graphic settings, including lowering texture quality to minimum.

If you use Galaxy, you can use it to verify installed files in check for damaged files.

I have gone from .06 and tried every patch since then. The graphics are all set to high.
I do not have galaxy, but I might give that a try.

Judging from your screenshot, those aren't even proper textures, they're placeholders the game puts before it loads the actual textures. Normally you shouldn't even see them, or maybe for a fraction of second only.
I guess you have a real bug on your hands, the textures aren't loading properly. Have you updated your graphic card's drivers recently? You might want to reinstall the latest drivers, or roll back to the last drivers before that. And you could also try reinstalling Witcher 3, or have Galaxy verify your installation, as the other guy suggested.

I'd go with Masodiks recommendation to update your graphic drivers. Go to Nvidia website, don't use their auto program, whatever it's called.

Having said that... doesn't Geralt look like he could lose a few pounds in you screenshot? lol

Thanks guys! I will try to make a clean install of my drivers when I get home. I have tried the last 4-5 drivers.
I will also install galaxy.

Brashen: Haha! That might be because he has been sitting still for a couple of mounths now :P

What I find pretty interesting about the screenshot is that some of the textures clearly has loaded (look at the trees in the background) which could suggest that the problem is not isolated to the textures alone but also depends on something else. Does this only happen on dynamic objects (characters, animals, items and such)?

This is true. I will take some more screenshots and post them here.

The issue might simply be that one of the container files for some of the assets are corrupt or deleted. This seems to be consistent with what you have experienced (only parts of the world is untextured / bugged). I would suggest that you back up you saves and verify installed files if you use Galaxy or reinstall the game if you don't (also make sure that the installer isn't corrupted - verify checksums here if you want to be certain).
Edit: It probably isn't corrupted as you were able to play normally in the beginning.

Thanks a bunch for the answer! I will try to install galaxy this weekend and see what happens.
You have been very helpfull!

Glad to be of help!
(But beware when installing Galaxy - it is still in beta. Also, it will download the whole game uncompressed over your internet connection (~35GB) it might not be an option if you are on capped or otherwise limited internet (in that case, you should probably try to reinstall it without Galaxy first)).