Tourists view Hukou Waterfall of the Yellow River in Yichuan County, northwest China's Shaanxi provinces, May 18, 2018. (Xinhua/Zhao Jie)

Tourists pose for photos at Hukou Waterfall of the Yellow River in Yichuan County, northwest China's Shaanxi provinces, May 18, 2018. (Xinhua/Zhao Jie)

Tourists view Hukou Waterfall of the Yellow River in Yichuan County, northwest China's Shaanxi provinces, May 18, 2018. (Xinhua/Zhao Jie)