Why has the Yangtze River Turned Red?
A stretch of China’s mighty Yangtze River, near the city of Chongqing, has turned an alarming shade of red…
Indeed, on 7 September the Chongqing Environmental Protection Agency noted on its website that a water-quality monitoring centre on the Yangtze had detected very high concentrations of silt in the river. The agency says that torrential rain in the upper Sichuan province caused huge amounts of silt to wash into the Yangtze. It also says that the water does not contain hazardous or noxious substances.
Scientists interviewed by Nature say that it is unlikely, although not impossible, that the colouring is a result of an algal bloom. Sudden growths of algae, fed by fertilizer run-off (a process known as eutrophication), can sometimes produce blooms of brownish diatom algae in rivers, says Sergi Sabater, a limnologist at the Catalan Institute of Water Research in Spain, who carries out research in river ecology. Such ‘red tides’ of algae are sometimes observed in warm, shallow and nutrient-rich seas.