The Rio Tinto is a river in the south-western part of Spain that rises  in the mountains of Andalusia. Since ancient times sections along the river have been mined for copper, silver, gold and other minerals. As a result, many mines and quarries were formed and the waters of the river were painted dark red and are rich in acid and heavy metals.

The Rio Tinto is known for its acidic water (pH 1.7-2.5) and a variety of heavy metals. More than 5000 years of mining have contributed to the pollution of the river turning the Tinto into an extremely dangerous place. Mining for copper stopped here in 1986, and silver and gold in 1996, but huge mines, quarries and excavations have remained, and metals continue to fall into the waters of the river.