Ulken-Karoy or Ulken Karaoy, meaning "Big Karoy" (Kazakh: Үлкен Қараой; Russian: Улькен-Карой or Большой Карой —Bolshoy Karoy),[1][2] is a salt lake in Akzhar District, North Kazakhstan Region, Kazakhstan.

[6] Lying in the southern part of the Ishim Plain, south of the Russian border, Ulken-Karoy is one of the main lakes of the region.

In years of drought Ulken-Karoy almost completely dries up and its water surface may decline to barely 5 square kilometers (1.9 sq mi).

It is joined to the mainland in its southern part, except during periods of high water.

[9] Ulken-Karoy lake is surrounded by a strip of salt marshes.