Qinghai Lake, formerly known as Koko Nur or Kukunor, is a saline lake situated in the province of Qinghai, and is the largest lake in China. The names Qinghai and Koko Nur both mean "Blue/Teal Sea/Lake" in Chinese and Mongolian. It is located about 100 kilometres (62 mi) west of the provincial capital of Xining at 3,205 m (10,515 feet) above sea level in a depression of the Tibetan Plateau in the cultural area known to ethnic Tibetans as Amdo. Twenty-three rivers and streams empty into Qinghai Lake, most of them seasonal. Five permanent streams provide 80% of total influx.

The lake has fluctuated in size, shrinking over much of the 20th century, but increasing since 2004. Despite its salinity, it has an abundance of fish, such as the edible naked carp (Gymnocypris przewalskii, huángyú (湟鱼)).

Qinghai Lake is sandwiched between Hainan and Haibei Tibetan Autonomous Prefectures in northeastern Qinghai. The lake is located at the crossroads of several bird migration routes across Asia. Many species use Qinghai as an intermediate stop during migration. As such, it is a focal point in global concerns of avian influenza (H5N1), as a major outbreak here could spread the virus across Europe and Asia, further increasing the chances of a pandemic. Minor outbreaks of H5N1 have already been identified at the lake. At the tip of the peninsula on the western side of the lake are the "Bird Islands" (Cormorant Island and Egg Island), which have been bird sanctuaries of the Qinghai Lake Natural Protection Zone since 1997. The lake often remains frozen for three months continuously in winter.