Koybagar (Kazakh: Қойбағар; Russian: Койбагар) is a lake in the Kostanay Region, Kazakhstan.

[1] Koybagar is a steppe lake of the central sector of the Turgay Basin in Karasu District, Kostanay Region.

[2][3][1] Koybagar is an endorheic lake lying in an isolated basin encircled by an unbroken wall of clay cliffs varying in height from 3 meters (9.8 ft) to 10 meters (33 ft).

It is located between the larger Kushmurun lake to the west and the smaller Tyuntyugur to the east.

[2][1] In years of heavy snowfall the lake may reach a surface area of 127 square kilometers (49 sq mi) and the water becomes fresh.