A single gallon of oil can result in an oil slick of up to 100 square meters. Large oil spills such as the Deepwater Horizon oil spill in the Gulf of Mexico in 2010 can result in hundreds of square miles of surface contamination, extensive pollution of coastal areas and estuaries and residual oil on the ocean floor for an extended period after the spill. As oil mixes with water, it forms a sticky substance called "mousse."
Oil spills can be extremely damaging to wildlife populations. Oil destroys the insulating properties of feathers and fur. When animals and birds become coated in oil, they often become susceptible to hypothermia. Many birds also become unable to float, and drown as a result. Oil that is ingested can sicken or kill an animal. As the oil remains in the local ecosystem, it bioaccumulates in food chains, disrupting reproductive cycles and resuting in greater incidence of illness. Oil also destroys marine plant life and coral reefs, reducing habitat for all creatures.
Humans living near an oil spill can face destruction of the economic base and a poisoning of local food supply. Many coastal communities rely on fishing and tourism for a large proportion of local economic activity. Oil spills can destroy local fisheries and severely diminish tourist traffic. Oil and other chemicals can remain in the local environment for many years, migrating gradually into local estuaries and deltas. The result is a more toxic environment for people, with related risks to public health.
Water bodies can also be affected by the actions taken in response to an oil spill. Oil dispersant chemicals have been particularly controversial. Corexit, which was used during the Exxon Valdez oil spill and the Deepwater Horizon spill, is a dispersant toxic to human and sea life. Toxicology studies have determined that Corexit can rupture red blood cells, and cause internal bleeding and organ damage. Because of the volumes of dispersant used to treat large spills, the chemicals will remain in the marine environment for many years, with unknown consequences.