Question: why sutlej is called red river?
Answer: The Real Himachal - GK The Sutlej is sometimes known as the Red River. It is the easternmost tributary of the Indus River. Its source is Lake Rakshastal in Tibet. From there, it flows at first west-northwest for about 260 kilometres (160 mi) to the Shipki La pass, entering India in Himachal Pradesh state.