Lake Zaysan or Zaisan, also known by other names in other languages, is a freshwater lake in Tarbagatay District, East Kazakhstan Region, Kazakhstan. It is the largest lake in the region. The lake is generally frozen from the beginning of November to the end of April, but still has an abundance of fish.

East Kazakhstan Region is a region of Kazakhstan. It occupies the easternmost part of Kazakhstan, and includes parts of the Irtysh River, Lake Markakol, and Lake Zaysan. Its administrative center is Öskemen. The region borders Altai Krai and Altai republic in Russia in the north and northeast and the People's Republic of China, via Xinjiang, in the south and southeast. The easternmost point of the Oblast is within about 50 kilometres of the westernmost tip of Mongolia; however, Kazakhstan and Mongolia do not share a common border, the two countries being separated by a small part of Russia and China.