Independent scientists and government officials say there's a disaster we can't see in the Gulf of Mexico's mysterious depths, the ruin of a world inhabited by enormous sperm whales and tiny, invisible plankton.

Researchers have said they have found at least two massive underwater plumes of what appears to be oil, each hundreds of feet deep and stretching for miles. Yet the chief executive of BP PLC - which has for weeks downplayed everything from the amount of oil spewing into the Gulf to the environmental impact - said there is "no evidence" that huge amounts of oil are suspended undersea.

BP CEO Tony Hayward said the oil naturally gravitates to the surface - and any oil below was just making its way up. However, researchers say the disaster in waters where light doesn't shine through could ripple across the food chain.

"Every fish and invertebrate contacting the oil is probably dying. I have no doubt about that," said Prosanta Chakrabarty, a Louisiana State University fish biologist.

On the surface, a 24-hour camera fixed on the spewing, blown-out well and the images of dead, oil-soaked birds have been evidence of the calamity. At least 20 million gallons of oil and possibly 43 million gallons have spilled since the Deepwater Horizon drilling rig exploded and sank in April.

That has far eclipsed the 11 million gallons released during the Exxon Valdez spill off Alaska's coast in 1989. But there is no camera to capture what happens in the rest of the vast Gulf, which sprawls across 600,000 square miles and reaches more than 14,000 feet at its deepest point.

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