The Rio Tinto river has a unique red and orange colour derived from its chemical makeup that is extremely acidic and with very high levels of iron and heavy metals.

[2] After the 50 kilometre mark, the chemistry that makes the Rio Tinto river so unique appears to slowly decline, as does the odd colouring.

[2] The river's chemistry begins to significantly change following the town of Niebla as the Rio Tinto blends itself with other streams that are connected to the Atlantic Ocean.

The Rio Tinto area has been the site of approximately 5,000 years of ore mining,[3] including copper, silver, gold, and other minerals,[4] extracted as far as 20 kilometres from the river shores.

[2] As a possible result of the mining, the Río Tinto is notable for being very acidic (pH 2) and its deep reddish hue is due to iron dissolved in the water.

The Rio Tinto region has been the source of approximately 5,000 years of ore extraction,[3] and chemical refinement primarily for copper, silver and gold, and later for iron, manganese and other minerals.

The presence of anaerobic bacteria in the sediments is thought to contribute somewhat to the river's famously low pH (acidity), that in turn increases the concentration of dissolved heavy metals.

[9] On the other hand, it is known that toxic water emanates from these vast underground and open pit mines and chemical ore refinement that had been active off and on for thousands of years.

[17] Likewise, the moon Europa contains an acidic[better source needed] ocean of water underneath its ice surface, thus the Rio Tinto river is of interest to astrobiologists studying the environmental limits of life and planetary habitability.