Hongjiannao National Nature Reserve, Nature reserve in Shenmu City, China.

Hongjiannao is a freshwater lake in the Muus Desert, under Erlintu Town, Shenmu City, Shaanxi. Its open water covered 67 km² in 1969, stayed between 50 and 60 km² for decades, fell below 30 km² by 2015, and recovered to 35 km² in 2020. The lake is the main habitat of the relict gull, with 95% of the world population breeding here.

The reserve was created to protect a rare gull species with its largest breeding population found nowhere else in the world at this scale. Conservation efforts have centered on safeguarding this endangered species.

The lake lies on the border between Shenmu in Shaanxi and Ejin Horo Banner in Inner Mongolia, and the two sides have repeatedly clashed over use of its land and water. Disputes that began as online arguments have escalated into confrontations between residents and police. The name Hongjiannao combines the Chinese words for red and alkali, referring to the lake's alkaline water.

Visit timing depends on the season, as different bird species are visible at different times throughout the year. Coordinating with local guides helps visitors plan their trip to see the species they wish to observe.

The lake is home to a particularly rare gull species that breeds here in concentrated numbers found nowhere else globally. This population represents a very large share of all remaining individuals worldwide.