Black oily sludge is seen on sand as cleaning operations continue at Ao Prao Beach on Koh Samet, Rayong July 31, 2013. An oil spill that has blackened beaches at the Thai holiday island of Koh Samet was having an extreme impact on tourism and could spread to the coast of the mainland and affect the fishing industry, officials and an environmental group said on Tuesday. REUTERS/Athit Perawongmetha (THAILAND - Tags: ENVIRONMENT DISASTER TRAVEL TPX IMAGES OF THE DAY)