Amu Darya or Amudarya, river, c.1,600 mi (2,580 km) long, formed by the junction of the Vakhsh and Pandj rivers, which rise in the Pamir Mts. of central Asia. It flows generally northwest, marking much of the northern border of Afghanistan with Tajikistan, Uzbekistan, and Turkmenistan before flowing through the Kara Kum desert of Turkmenistan and Uzbekistan, and entering the S Aral Sea through a delta. The river drains c.180,000 sq mi (466,200 sq km). It flows swiftly until it reaches the Kara Kum where its course braids into several channels. The Amu Darya provides water for irrigation, but this heavy draw on its water has prevented the Amu Darya from replenishing the Aral Sea. The Kara Kum Canal (c.500 mi/800 km long) carries water from the Amu Darya near Kelif across S Turkmenistan to Ashgabat and supplements the flow of the Tejen and Murgab rivers. The Amu Darya is paralleled by the Trans-Caspian RR, which has lessened the river's importance as a transport route. In ancient times the Amu Darya was called the Oxus and figured importantly in the history of Persia and in the campaigns of Alexander the Great.