Rio Tinto Andalusia

The Río Tinto , red river or Tinto River) is a highly toxic river in southwestern Spain that rises in the Sierra Morena mountains of Andalusia. It flows generally south-southwest, reaching the Gulf of Cádiz at Huelva. The Rio Tinto river has a unique red and orange colour derived from its chemical makeup that is extremely acidic and with very high levels of iron and heavy metals.]

The river maintains its colour for an approximate length of 50 kilometres.After the 50 kilometre mark, the chemistry that makes the Rio Tinto river so unique appears to slowly decline, as does the odd colouring. The location where the chemistry of the river is altered is near a town called Niebla. The river's chemistry begins to significantly change following the town of Niebla owing to the fact that the Rio Tinto blends itself with other streams that are connected to the Atlantic Ocean. The river is approximately 100 km (62 mi) long and is located within the Iberian Pyrite Belt. This area has large amounts of ore and sulfide deposits.

The Rio Tinto area has been the site of approximately 5,000 years of ore mining, including copper, silver, gold, and other minerals, extracted as far as 20 kilometres from the river shores. As a possible result of the mining, the Río Tinto is notable for being very acidic and its deep reddish hue is due to iron dissolved in the water. Acid mine drainage from the mines leads to severe environmental problems because the acidity (low pH) dissolves heavy metals into the water. It is not clear how much acid drainage has come from natural processes and how much has come from mining. There are severe environmental concerns over the pollution in the river.

Although the river represents a harsh environment for life, some microorganisms classified as extremophiles do thrive in these conditions. Such life forms include certain species of bacteria, algae and heterotrophs.
(text from Wikipedia)