When the streams Biya and Katun join in Altai Krai, they form this mighty river. It is located in West Siberia, Russia and has many names- the Siberian Tatars call it Omar or Umar, the Samoyedes- Kolta or Kuay and to the Ostiaks it is known as the As, Yag, Kolta and Yema. It joins the Irtysh river, forming the longest river flow in Russia. What is its name?