Spain's Toxic Red River

The Río Tinto is a highly toxic river in southwestern Spain. It rises in the Sierra Morena mountains of Andalusia.

Dissolved iron gives the water a deep red colour. The river maintains this hue for 50 kilometres.

The river has a distinctive hue unlike most rivers.

People have mined copper, silver and gold here for 5,000 years. Ore was extracted 20 kilometres from the shores.

The water is extremely acidic with a pH of 2. This acidity dissolves heavy metals into the flow.

Anaerobic bacteria feed on iron and sulphide minerals in the rocks. Their metabolism produces ferric iron and acidic liquid.

Commercial copper production restarted in February 2016. The mine would employ 350 people during its startup phase.

Scientists compare the river to groundwater on Mars. Astrobiologists study these extreme conditions to understand planetary habitability.