Oil spills affect water in a variety of ways. When oil is released into water, it does not blend with the water. Oil floats on the surface of salt and fresh water. Over a very short period of time, the oil spreads out into a very thin layer across the surface of the water. This layer, called a slick, expands until the oil layer is extremely thin. It then thins even more. This layer is called a sheen and is usually less than 0.01 mm thick.
Oil spills on the surface of the water are subjected to the whims of weather, waves and currents. All these natural forces move slicks across the surface of the water. In addition, these forces stir up the oil slick and also control the direction the slick moves in. An oil spill far out at sea can be carried ashore by wave and current action. Rough seas can split an oil slick apart, carrying some oil in one direction and more in another. In contrast, a near shore oil spill can be totally controlled by currents and wave action that causes the oil to come ashore, damaging marine shoreline habitat.
Different types of oil react differently when spilled. Some evaporate in small amounts, while others break down quicker. After the sheen breaks down, a moderate amount of oil will break down and be deposited on the bottom of the ocean. This usually happens in shallow water. Certain types of microbes will break apart and consume the oil, but this in no way makes up for the damage done during the spill. In addition, when oil breaks apart and sinks to the ocean floor, it contaminates the underwater habitat, too.