2. Spain Rio Tinto

The vast mines of Rio Tinto give a hypnagogic, almost martian landscape. Its growth has consumed not only mountains and valleys but even entire villages. This river has gained recent scientific interest due to the presence of extremophile aerobic bacteria that dwell in the water.The extreme conditions in the river are analogous to other locations in the solar system thought to contain liquid water, such as subterranean Mars. Río Tinto is notable for being very acidic (pH 2) and its deep reddish hue. It is metal solvent and surely not human-friendly!