Zhamantuz () is a salt lake in the Zhangeldi District, Kostanay Region, Kazakhstan.
The lake lies to the south of Kokalat town. The name Zhamantuz, meaning "bad salt" in the Kazakh language, is of nomadic origin.
Zhamantuz is an endorheic lake of the Turgay Depression. It is part of the Turgay river basin. The lake lies at an elevation of . The Turgay flows about to the northwest of the lake.
Zhamantuz has an elongated shape, stretching for over in a northeastâÂÂsouthwest direction. The lake fills yearly with rain and snow and rarely freezes in the winter. Zhamantuz is an intermittent lake that dries in the summer.
Zhamantuz is known as a "dead lake" () in Kazakh owing to the lack of fish living in its bitter waters. Typha and Phragmites reeds grow in stretches of the lakeshore and wormwood tufts close around the basin.