A section of the Yellow River turned red and smelly in Lanzhou, capital of northwest China's Gansu Province, and the local environment watchdog has launched an investigation. Residents were alarmed to see a sewage pipe pouring red water into the country's second longest river between 3 pm and 6 pm Sunday. The discharge occurred near a park by Nanbinhe Road in down-town Lanzhou. About a kilometre of the river was discoloured.