Valmiki Ramayana Ayodhya Kanda Sarga 63 Shloka 19

विमलान्यपि as though the waters were pure, स्रोतांसि the rapid flow, गिरिधातुभ्यः of mineral ores, सभस्मानि mixed with ashes, पाण्डुरारुणवर्णानि white and red in colour, भुजङ्गवत् like a serpent, सुस्रुवुः flowed.

Although pure, the rapidly flowing water from the mountains mixed with the minerals in the soil turned white and red in colour and flowed like a serpent.