A boat is seen on the Yellow River at the Heishan Gorge area in Zhongwei City, northwest China's Ningxia Hui Autonomous Region, Apirl 29, 2014. (Xinhua/Li Ran)

Photo taken on April 29, 2014 shows the scenery of the Yellow River at the Heishan Gorge area in Zhongwei City, northwest China's Ningxia Hui Autonomous Region. (Xinhua/Li Ran)

Photo taken on April 29, 2014 shows the scenery of the Yellow River at the Heishan Gorge area in Zhongwei City, northwest China's Ningxia Hui Autonomous Region. (Xinhua/Li Ran)

A tourist poses for photos beside the Yellow River at the Heishan Gorge area in Zhongwei City, northwest China's Ningxia Hui Autonomous Region, Apirl 29, 2014. (Xinhua/Li Ran)

Photo taken on April 29, 2014 shows the scenery of the Yellow River at the Heishan Gorge area in Zhongwei City, northwest China's Ningxia Hui Autonomous Region. (Xinhua/Li Ran)