An egret flies over the 1,500-hectare Mai Po nature reserve in Hong Kong neighbouring mainland China's southern city of Shenzhen (background) in this November 12, 2004 file photo. As an important nature reserve for migratory birds in the territory, Mai Po is being increasingly polluted and choked up by industrial and organic waste flushed down from southern China, a leading green group said on February 27, 2007. Picture taken November 12, 2004.