Lake Issyk Kul is 182 km long, up to 61 km  wide, 702 meters deep, 
6236 square kilometers at an altitude of 1608 meters. 
Water is very clear, visibility until 20 meters depth.
Surrounded by 4km mountains

From south east. Rivers only come to lake ...

... and no rivers leave lake. From north

From south. Water is salty, not drinkable.