Photo taken on Sept. 24, 2011 shows villagers herd cattle on the riverbed of China's largest desert lake Hongjiannao in Yulin, north China's Shaanxi Province. Hongjiannao is shrinking as a result of climate change and human activities, and may vanish in a few decades. Its lake area, which measured more than 6,700 hectares in 1996, has shrunk to 4,180 hectares. Its water level is declining by 20-30 centimeters annually and its water PH value has risen to 9.0-9.42 from 7.4-7.8.