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Today marks four years since the deepwater horizon oil rig explosion in the Gulf of Mexico — which led to the worst environmental disaster in U.S. history.

On April 20th, 2010, an oil rig operated by British Petroleum exploded, killing eleven employees and spilling nearly five-million barrels of crude oil into the Gulf of Mexico.

The spill was eventually capped in July 2010 — 87 days after more than 200 million gallons of oil leaked into the Gulf.