Air and water pollution are caused by the release of harmful substances into the environment. Air pollution comes from burning fossil fuels which releases gases and chemicals. Smog is a type of air pollution caused by smoke from coal burning. The Great Smog of London in 1952 resulted from industrial pollution and weather, killing thousands. Water pollution occurs when chemicals contaminate bodies of water, degrading quality. The Jiyeh power plant oil spill in 2006 leaked 30,000 tons of oil into the Mediterranean sea after the plant's tanks were bombed. Prevention efforts include reducing vehicle and fireplace use, properly disposing waste, and reporting polluters.