The two most important rivers in northern Tajikistan are the Syr Darya and the Zeravshan (Zarafshan). The former, the second longest river in Central Asia with a total length of , stretches across the Fergana Valley in far-northern Tajikistan. The Zeravshan River, with a total length of , runs for through the north-center of Tajikistan. Tajikistan's rivers reach high-water levels twice a year: in the spring, fed by the rainy season and melting mountain snow, and in the summer, fed by melting glaciers. The summer freshets are the more useful for irrigation, especially in the Fergana Valley and the valleys of southeastern Tajikistan. Most of Tajikistan's lakes are of glacial origin and are located in the Pamir region in the eastern half of the country. The largest, the Karakul (Qarokul) Lake, is a salt lake devoid of life, lying at an elevation of . Tajikistan's second largest water body is the Kayrakum Reservoir, a long artificial lake in the heart of the Fergana Valley, not far from the city of Khujand in Sughd Province. The lake is fed by the Syr Darya. Another well-known natural lake of glacial origin is Iskanderkul. It is smaller than the Kayrakum Reservoir and lies in the Fann Mountains in western Tajikistan.