Most people mistakenly think that the main source of water pollution comes from organic matters. The truth is the organic matters are naturally decomposed by groups of aerobic bacteria. The bacteria uses oxygen dissolved in the water to decompose the organic matters. The process goes well when there’s enough oxygen in the water. The decomposed organic matters are then turned to be food for aquatic plants.
However, once the water is contaminated with grease, the grease covers the surface of the water. As a result, oxygen fails to reach the water. When there’s not enough oxygen in the water, the aerobic bacteria can’t work anymore, causing the anaerobic bacteria to take place and cause toxic gases such as Methane, Hydrogen Sulphide and Ammonia. These gases cause smells and color change and toxic, and cause the water to turn dark and smelly.