🇵🇪Red River in the valleys of Cusco, Peru

The red color of the river is a seasonal phenomenon.

Scientists have found out that the acquired color is a consequence of the flow of mountain waters through a valley saturated with many different minerals. 

In particular, we are talking about iron oxide, because it lies in large quantities under the soil.
https://earth.google.com/web/search/Palcoyo+Rainbow+Mountain