When a BP oil rig exploded and sank in the Gulf of Mexico last April, killing 11 workers, authorities first reported that no crude was leaking into the ocean.

They were wrong.

The disaster that captivated the world’s attention for 153 days struck at 9:53 p.m. CDT on April 20, when a surge of methane gas known to rig hands as a “kick” sparked an explosion aboard the Deepwater Horizon rig as it was drilling the mile-deep Macondo 252 well off Louisiana’s coast. Two days later, the rig sank.

One year on, oil from the largest spill in U.S. history clogs wetlands, pollutes the ocean and endangers wildlife, not to mention the toll it has inflicted on the coastal economies of Florida, Mississippi, Alabama and especially Louisiana.

It was the biggest ever accidental release of oil into an ocean.