Furthermore, improperly disposed used oil is a hazardous waste. Oil poured into the ground or into a storm drain will eventually find its way to the nearest stream or river and ultimately contaminate groundwater. Oil pollution can be extremely detrimental to aquatic ecosystems. Fish can be smothered by oil coating their gills or can be killed indirectly by reduced resistance to infection. Bottom-dwelling organisms such as oysters and clams can be smothered directly by settling of oil suspensions or indirectly by the reduced oxygen levels caused by coating of the water surface.
Oil can stunt or kill marsh vegetation or submerged grasses.
In addition to initial effects, once the oil begins to dissolve, toxics can be released, exposing marine organisms to potentially carcinogenic matter. It does not take a large quantity of oil to cause serious damage. The four quarts of oil it takes to fill your car's engine can form an oil slick nearly eight acres in size. It takes little imagination to picture the damage caused when one person dumps oil down a storm drain. Remember, you lose when you don't recycle used oil.