Lake Issyk-Kul, a drainless lake in the northern Tien Shan mountains of Kyrgyzstan, is one of the largest mountain lakes in the world, and is famous for its magnificent scenery and unique scientific interest. It spans an area of approx. 6300 km2, is roughly 750 m deep and its surface is at an elevation of about 1700 m. The lake's name (derived from a word for "hot lake") gives a hint on the fact that it does not freeze during the winter despite its elevation. Air temparatures in summer are about 16°C, while in winter they do not go below -3°C.
Lake terraces along the shores indicate a higher water level in the past. The presence of underwater ruins of buildings proves that in the Middle Ages the level of the lake was lower than it is now. In the 20th century the lake has dropped more than three meters. Seasonal fluctuations of the level, caused by summer floods in the approx. 50 rivers of the Issyk-Kul basin, range from 20 to 60 cm. Surface curents, which flow counterclockwise, have been recorded. The water of the Issyk-Kul is sky blue in colour, very clear (visibility up to 65 feet), and salty (0.6%).