@ Slobodan Blagojevic, Hidden Grid, thierrylegros396 - thank you for your comments
@ Paulo Bizarro - sadly the reason is the same, it is a mine lake of a nearby copper mine (picture 4)
@ spidermike - I think I wasn't explicit enough. I observed that many times we are quite passive regarding environmental problems. And this is partly because of the presentation of the subject. In this actual case, first time when I saw the b&w versions, the scene looked quite nice, I can even say idyllic. Nice hills with a lake, meadow with some basic agriculture, and in the background, but quite far, some industrial activity. But when you see the color pictures, everything becomes unnatural, and you realize that the pictures show a very serious environmental issue.
@ Mike D. B. - as Slobodan said, only the other way, I wanted first the b&w, and with mouse over the color versions.