Aerial photo taken on May 20, 2019 shows the scenery of the three gorges of the Yellow River in Yongjing County, northwest China's Gansu Province. The three gorges that consist of Bingling Gorge, Liujia Gorge and Yanguo Gorge are located at the upper reaches of the Yellow River, China's second largest river. (Photo: Xinhua)

Aerial photo taken on May 20, 2019 shows the scenery of the three gorges of the Yellow River in Yongjing County, northwest China's Gansu Province. The three gorges that consist of Bingling Gorge, Liujia Gorge and Yanguo Gorge are located at the upper reaches of the Yellow River, China's second largest river. (Photo: Xinhua)

Photo taken on May 20, 2019 shows the scenery of the three gorges of the Yellow River in Yongjing County, northwest China's Gansu Province. The three gorges that consist of Bingling Gorge, Liujia Gorge and Yanguo Gorge are located at the upper reaches of the Yellow River, China's second largest river. (Photo: Xinhua)

Aerial photo taken on May 20, 2019 shows the scenery of the three gorges of the Yellow River in Yongjing County, northwest China's Gansu Province. The three gorges that consist of Bingling Gorge, Liujia Gorge and Yanguo Gorge are located at the upper reaches of the Yellow River, China's second largest river. (Photo: Xinhua)

Tourists glide above the three gorges of the Yellow River in Yongjing County, northwest China's Gansu Province, May 19, 2019. The three gorges that consist of Bingling Gorge, Liujia Gorge and Yanguo Gorge are located at the upper reaches of the Yellow River, China's second largest river. (Photo: Xinhua)

Photo taken on May 20, 2019 shows the scenery of the three gorges of the Yellow River in Yongjing County, northwest China's Gansu Province. The three gorges that consist of Bingling Gorge, Liujia Gorge and Yanguo Gorge are located at the upper reaches of the Yellow River, China's second largest river. (Photo: Xinhua)

Aerial photo taken on May 20, 2019 shows the scenery of the three gorges of the Yellow River in Yongjing County, northwest China's Gansu Province. The three gorges that consist of Bingling Gorge, Liujia Gorge and Yanguo Gorge are located at the upper reaches of the Yellow River, China's second largest river. (Photo: Xinhua)

Aerial photo taken on May 20, 2019 shows the scenery of the three gorges of the Yellow River in Yongjing County, northwest China's Gansu Province. The three gorges that consist of Bingling Gorge, Liujia Gorge and Yanguo Gorge are located at the upper reaches of the Yellow River, China's second largest river. (Photo: Xinhua)