From Kyrgyz Ысык-Көл (Isık-Köl) "hot lake" via Russian Иссык-Куль (Issyk-Kúlʹ)
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Wiktionary
Issyk-kul Sentence Examples
Southwards from the last-named, however, at the foot of the mountains and at the entrance to the valleys, there are rich areas of fertile land, which are being rapidly colonized by Russian immigrants, who have also penetrated into the Tian-shan, to the east of Lake Issyk-kul.
Lake Balkash, or Denghiz, Lake Ala-kul (which was connected with Balkash in the post-Pliocene period, but now stands some hundred feet higher, and is connected by a chain of smaller lakes with Sissyk-kul), Lake Issyk-kul and the alpine lakes of Son-kul and Chatyr-kul are the principal sheets of water.
It forms the barrier between the Issyk-kul and Balkash lakes, the elevation of which is about 5000 ft.