Valmiki Ramayana Yuddha Kanda Sarga 75 Shloka 30

लङ्कायाम् in Lanka, दह्यमानायाम् while burning, छायासंसक्तसलिलः the image of reflected in water, महार्णवः of the ocean, लोहितोदः red coloured, महार्णवःइव like ocean, शुशुभे appeared.

While Lanka was burning its image reflected in the ocean made the ocean look like an ocean of red waters.