Issyk-Kul is an endorheic saline lake in the western Tianshan Mountains in eastern Kyrgyzstan, just south of a dividing range separating Kyrgyzstan from Kazakhstan. It is the seventh-deepest lake in the world, the tenth-largest lake in the world by volume, the deepest lake whose deepest point is above sea level, and the third-largest saline lake. Issyk-Kul means "warm lake" in the Kyrgyz language; although it is located at a lofty elevation of 1,607 metres (5,272 ft) and subject to severe cold during winter, it rarely freezes over due to high salinity.

An endorheic basin is a drainage basin that normally retains water and allows no outflow to other, external bodies of water ; instead, the water drainage flows into permanent and seasonal lakes and swamps that equilibrate through evaporation. Endorheic basins are also called closed basins, terminal basins, and internal drainage systems.