The Río Tinto is a river in southwestern Spain that originates in the Sierra Morena mountains of Andalusia. It flows generally south-southwest, reaching the Gulf of Cádiz at Huelva.
Since ancient times, a site along the river has been mined for copper, silver, gold, and other minerals. In approximately 3,000 BC, Iberians and Tartessians began mining the site, followed by the Phoenicians, Greeks, Romans, Visigoths, and Moors. After a period of abandonment, the mines were rediscovered in 1556 and the Spanish government began operating them once again in 1724. As a possible result of the mining, Río Tinto is notable for being very acidic (pH 2) and its deep reddish hue is due to iron dissolved in the water. Acid mine drainage from the mines leads to severe environmental problems due to the heavy metal concentrations in the river. In 1873, the multinational Rio Tinto Company was formed to operate the mines; by the end of the 20th century it had become one of the world's largest mining companies, although it no longer controls the Rio Tinto mines; these are now owned by EMED Mining plc.