Rio Tinto algae. Light microscopy footage of algae in a sample of water from the Rio Tinto river in Spain. This river flows through an area rich in minerals, and contains extremophile bacteria that feed on iron and sulphide minerals, creating an acidic environment. Over many kilometres this river has a pH of 2 and the reddish tint for which it is named. Despite the toxic environment, this river contains many microbe and algae species that are adapted to survive in such conditions.