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.

The Ashchisu and Karasu are the main rivers flowing into the lake.