Kushmurun (Kazakh: Құсмұрын; Russian: Кушмурун) is a brackish lake in the Kostanay Region, Kazakhstan.

It lies in the northern sector of the Turgay Basin, at the border between Auliekol and Karasu districts, 9 kilometers (5.6 mi) north of the village of Kushmurun.

The lake stretches roughly from SSW to NNE and is crossed by the Ubagan river, a right tributary of the Tobol, from south to north.

[4] The bottom of Kushmurun is flat and has thick strata of clay and loam sediments covered with layers of silt.

[5][2] Kushmurun lake was a refuge for aquatic birds and waders that used to thrive in the formerly extensive reedbeds of the lakeshore.