Black-headed gulls rest on the Dianchi Lake, the largest fresh water lake on the Yunnan-Guizhou Plateau, in Kunming, capital of southwest China's Yunnan Province, Jan. 20, 2019. Water quality in the Dianchi Lake rose to grade IV in 2018, the best in the recent 30 years, after a series of restoration measures. (Xinhua/Lin Yiguang)