Kyzylkak (Kazakh: Қызылқақ; Russian: Кызылкак) is a bittern salt lake in Ertis District, Pavlodar Region, Kazakhstan.

The nearest inhabited locality is Kyzylkak village, located 3 kilometers (1.9 mi) to the south of the southern coastline of the lake.

[3][4] Kyzylkak is an endorheic lake located in the Ishim Plain, south of the Russian border.

The bottom of the lake has a thick layer of black mud containing magnesium salts and releasing Hydrogen sulphide.

[5] Lake Kyzylkak is fed mainly by snow, but owing to its high salinity it does not freeze in the winter.