Aerial photo taken on Jan. 20, 2019 shows the Dianchi Lake, the largest fresh water lake on the Yunnan-Guizhou Plateau, in Kunming, capital of southwest China's Yunnan Province. 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/Hu Chao)