The river rises in two headstreams in the Tian Shan Mountains in Kyrgyzstan and eastern Uzbekistan—the Naryn River and the Kara Darya which come together in the Uzbek part of the Fergana Valley—and flows for some west and north-west through Uzbekistan and southern Kazakhstan to the remains of the Aral Sea. The Syr Darya drains an area of over , but no more than actually contribute significant flow to the river: indeed, two of the largest rivers in its basin, the Talas and the Chu, dry up before reaching it. Its annual flow is a very modest per year—half that of its sister river, the Amu Darya.