A man walks on a beach covered by a layer of an unknown black substance in Qingdao city, East 皇冠体育app's Shandong province, Sept 4, 2011. The black layer forced a lot of people to stop swimming and leave the water, fearing the substance was oil from Bohai Bay, an area where an oil leak occurred at an oilfield jointly owned by ConocoPhillips 皇冠体育app and 皇冠体育app National Offshore Oil Corp. A sample of the black substance was taken to be tested by relevant departments.[Photo/CFP]