Rio Tinto (river)

The Río Tinto (Spanish pronunciation: [ˈri.o ˈtinto], 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 Río Tinto river has a unique red and orange colour derived from its extremely acidic chemical makeup with very high levels of iron and heavy metals. The name río tinto means "coloured river" in Spanish, in contrast to most rivers, which are clear. However, "tinto" is also an expression for red wine in Spain, so it is also related to this second meaning.

The river maintains its colour for approximately 50 kilometres. After 50 kilometres, its unique chemistry appears to slowly subside, along with the odd colouring. The acidic content of the river is altered near the town of Niebla. The acid begins to be neutralized past the town of Niebla as the Río Tinto blends with other streams flowing into 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 sulphide deposits.

The Río Tinto area has had 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 very acidic (pH 2) with its deep reddish hue 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 is from natural processes and how much has come from mining. There are severe environmental concerns over the river pollution.

Although the river is a harsh environment, some microorganisms classified as extremophiles do thrive in these conditions. Such life forms include certain species of bacteria, algae and heterotrophs.