Locals swim in the Erhai Lake in Bai Autonomous Prefecture of Dali, southwest China's Yunnan Province, June 6, 2010. Erhai Lake, covering 253 square kilometers and being the second largest fresh water lake in Yunnan Province, is named as the "mother lake" by local people. Thanks to the efforts of local government in controlling pollution in the famous plateau lake and improving the local environment, the water quality of the lake has been improved. [Xinhua]