There appears to be a little contraversy over the images, but it looks like the real thing -- you can even see ripples in the water and small stones through it.
A new analysis of pictures taken by the exploration rover Opportunity reveals what appear to be small ponds of liquid water on the surface of Mars.
The report identifies specific spots that appear to have contained liquid water two years ago, when Opportunity was exploring a crater called Endurance. It is a highly controversial claim, as many scientists believe that liquid water cannot exist on the surface of Mars today because of the planet’s thin atmosphere.
If confirmed, the existence of such ponds would significantly boost the odds that living organisms could survive on or near the surface of Mars, says physicist Ron Levin, the report's lead author, who works in advanced image processing at the aerospace company Lockheed Martin in Arizona.
Update: Looks like they're wrong. According to this site, it's probably just silt:
It's pretty easy to debunk this... just start off with a raw blue-biased 257 of the area... find a nearby rock imaged in 456'o-colour, and then use it as a baseline for balancing up the 257... do that and you get something a bit like this, not scientific, not accurate, but makes the cool clear, blue waters of Barsoom evaporate faster than Paris Hilton's hopes of another early release...
http://space.newscientist.com/article/dn12026-mars-rover-finds-puddles-on-the-planets-surface.html
