Millions of gallons of oil have been leaking into the Gulf of Mexico since the Deepwater Horizon oil rig disaster on 20 April 2010.
Despite efforts to stem the leak and contain the oil on the surface, the slick has spread, threatening wildlife and closing down 78,000 sq miles of the gulf to fishing.
Experts from several US federal agencies are tracking the spread of the slick and predicting its path using remote sensing equipment, reconnaissance flights and satellite imagery. Data and maps from their research are available online.
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