Sunset over the Hongjiannao Lake. [Photo provided to China Daily]

China's largest desert freshwater lake is in danger of drying up, experts have warned.

Hongjiannao Lake, on the border between Shaanxi province's Shenmu county and Ejin Horo Banner in the Inner Mongolia autonomous region, has shrunk significantly in recent years, according to the Shenmu county government.

The water quality has also deteriorated, leaving the lake almost devoid of fish life and hitting the local population of relict gulls, which are classified as vulnerable by the International Union for the Conservation of Nature.

According to information issued by the county government, the surface area of the lake has decreased from 67 sq km in 1969 to 32.8 square kilometers today.

Since 2006, the water level of the lake has dropped by 30 cm to 60 cm annually, and the average water depth has dropped from 8.2 meters to less than 4 meters.

Data provided by Shaanxi Provincial Water Conservancy Department also shows that the pH value of the lake has now reached 9.8, making the water too alkaline to support most life. As a result, 17 species of wild freshwater fish, which originally lived in the lake, have now vanished.

As the lake disappears, an islet in its middle that was previously used by gulls to breed has become a peninsula, said Xiao Hong, researcher with the Northwest Institute of Endangered Animals.

Consequently, the population of relict gulls at Hongjiannao has declined from 7,700 nesting pairs in 2011 to just 2,000 last year.

At the present rate of decline, the lake will dry up entirely within 10 years, said Huo Xueqi, assistant to the president of the Northwest Agriculture and Forestry University.