A wild yak is seen at the source of the Yellow River section of the Sanjiangyuan National Park in northwest China's Qinghai Province, Jan. 21, 2020. Sanjiangyuan, meaning the "source of three rivers," is home to the headwaters of the Yangtze, Yellow and Lancang rivers. The ecological system has been steadily improving in recent years in the Sanjiangyuan National Park, making it a habitat of an increasing number of wild animals. (Photo by Song Zhongyong/Xinhua)