Fish in Hongjiannao Lake, China's largest desert freshwater lake, are teetering on the verge of extinction, according to local fishery authorities.

"The fish in Hongjiannao have nearly vanished," said Li Weiping, the head of a fish monitoring station in northwest China's Shaanxi province.

As the lake continues to shrink, its water has become more salty and its pH reading has reached 9.6, while the maximum reading suitable for fish is 8.5, according to Li.

The lake has gradually lost the water that it used to get from underground streams and rivers, Li said, adding that excessive coal mining around the lake has changed the way water flows underground. Two reservoirs have been built on two rivers near the upper reaches of the lake, preventing river water from flowing into the lake.

The lake's water level has plunged by 20 to 30 centimeters every year. Its total surface area has been reduced to 41.8 square km, down from 67 km in 1996.