File photo taken on Feb. 16, 2017 shows black-necked cranes at the Dashanbao state nature reserve of black-necked cranes in Zhaotong, southwest China's Yunnan Province. To keep Yangtze River clean and beautiful, efforts to restore ecological environment have been taken in the upper reaches of Yangtze River in Yunnan Province in recent years. (Xinhua/Lin Yiguang)