What gives the Río Tinto in southwestern Spain its colour?

Question

What is prohibited by an unusual law that has been passed in Lanjarón, Spain, in three settlements in southern France: (Cugnaux, Le Lavandou & Sarpourenx), and has been proposed for Biritiba-Mirim, Brazil?

Answer 1

High levels of iron and heavy metals
For about the first fifty kilometres after the river rises in the Sierra Morena mountains of Andalusia - about half its total length - and until tributaries dilute the waters, the Rio Tinto river has a unique red and orange colour. The Rio Tinto area has been the source of approximately 5,000 years of ore mining, including copper, silver, gold, and other minerals.