This is a beautiful waterfall (about 50 meters?) close to Caviahue, a small and lovely town located in the north of Neuquén Province in Argentina.
The colors of these sulfurous waters are incredible... and as you can see, they affect the colors on the volcanic rocks around this place.
This version includes a really nice rainbow. To say the truth I came to this place twice, first time was about 6pm and noticed that light would be better earlier, so I returned next day at 11am! :)
Note: click on the image to see it @ Flickr (here I've added border and played with curves a bit).