When the crude petroleum covers the water surface, this deprives the ocean of sun light. In addition oil will collect on the wings of bird life which prevents them from flying. The birds have to be cleaned with a detergent substance to remove the oil from its feathers. The containment of the oil slick is very difficult. Wind conditions can quickly spread or move a slick making it almost impossible to contain.
Special skimmers have to be used once the oil slick has been cornered.
Recently, special cultured microbes have been used that digest the oil and allows the slick to be broken up into smaller more manageable slicks. Once the slicks have been reduced in size other detergent containing agents can further break down the slick. Eventually, the oil must be removed by physical skimming. In the future these special microbes might be used to totally consume oil slicks. Another danger is the burning of an oil rig.