At the mouth of the Yangtze River in Qidong, Jiangsu Province, fine sediment rich in organic matter and minerals has accumulated over time in an oxygen-deprived environment. The reduction of iron compounds within the sediment has gradually turned the tidal flats black.

Recently, this dark shoreline has transformed into a stunning “sky mirror.” As the tide recedes, a thin layer of water remains on the flats, creating the appearance of a vast mirror stretching between earth and sky. Pools of water shimmer with the golden glow of the setting sun, while drifting clouds and gentle ripples merge sky and sea into a single scene. Reflections of clouds, twilight, and beachgoers appear with remarkable clarity, blurring the boundary between reality and illusion and lending the coastal wetlands a uniquely poetic charm.