The most important river is the Ili, which enters Zhetysu from the Tian Shan mountains of China's Ili Kazakh Autonomous Prefecture in northern Xinjiang, and drains it for 250 km before it enters Lake Balkhash. The Chu River also rises in the Tian Shan mountains and flows north-westwards through the former Akmolinsk province of the Governor-Generalship of the Steppes. The Naryn River flows south-westwards along a longitudinal valley of the Tian Shan, and enters the Fergana Valley to join the Syr Darya. The major lakes of the area include Lake Balkhas (or Denghiz) and Lake Ala Kul, which was connected with Balkash in the post-Pliocene period but now stands some hundred feet higher, connected by a chain of smaller lakes with Sissyk Kul, Lake Issyk-Kul, and the alpine lakes of Son-Kul and Chatyr-Kul.