Because the high peaks function as moisture catchers, Kyrgyzstan is relatively well watered by the streams that descend from them. None of the rivers of Kyrgyzstan are navigable, however. The majority are small, rapid, runoff streams. Most of Kyrgyzstan's rivers are tributaries of the Syrdarya, which has its headwaters in the western Tian Shan along the Chinese border. Another large runoff system forms the Chui River, which arises in northern Kyrgyzstan, then flows northwest and disappears into the deserts of southern Kazakhstan. Ysyk-Köl is the second largest body of water in Central Asia, after the Aral Sea, but the saline lake has been shrinking steadily, and its mineral content has been rising gradually. Kyrgyzstan has a total of about 2,000 lakes with a total surface area of , mostly located at altitudes of 3,000 to 4,000 meters. Only the largest three, however, occupy more than each. The second- and third-largest lakes, Songköl and Chatyr-Köl (the latter of which also is saline), are located in the Naryn River Basin.