US scientists have charted vast oil plumes from the gushing BP well beneath the surface of the Gulf of Mexico, and warn that the impact of the "invisible" undersea oil may be felt for years.
"The public is seeing just a small fraction of what is taking place out there. Most of the oil is under the surface," Larry Schweiger, president and chief executive officer of the National Wildlife Federation, told AFP.
Schweiger had just returned from a 10-hour boat trip to the area near where the BP-leased Deepwater Horizon rig sank to the bottom of the Gulf in April, rupturing a riser pipe on an underwater well which has been spewing crude into the sea ever since.
Scientists on the vessel sent down a deep-water diving camera that records what is happening under the water, said Schweiger.
The images they saw looked "almost like an oil and vinegar mixture -- just like you have in a salad dressing with oil bubbles," said Schweiger.
"That's what it looks like under the Gulf where the water has been contaminated... We're looking at an area of around 150 miles that's contaminated with this sub-surface oil," Schweiger said, warning that the oil "will not go away tomorrow or anytime soon."
The area hit by the spill provides the United States with half its shrimp and oysters, more than a third of its blue crab, and a quarter of all its fin fish, said Schweiger.
"We have contaminated our seafood basket," said Schweiger.
At least four research groups from different US universities have reported finding massive plumes deep beneath the surface of the Gulf.
Researchers from the University of South Florida reported that they found "a wide area with elevated levels of dissolved hydrocarbons throughout the water column, possibly indicating that a limb of an undersea oil plume has spread northeast toward the continental shelf."
University of Georgia marine scientists reported two weeks ago finding deepwater plumes thousands of feet below the surface in the Gulf of Mexico.
The other two universities that have reported finding plumes are Louisiana State University and the University of Southern Mississippi.
But after the scientists went public with what they have found under the sea, BP chief executive Tony Hayward said that studies carried out by the British oil company found "no evidence" of underwater plumes of oil.
BP has sprayed nearly one million gallons of dispersant on the spill, Coast Guard Admiral Thad Allen said Thursday.
Steven Pedigo, head of Oil Spill Eater International, which manufactures a product that has been used to clean up thousands of oil spills in 20 countries, without dispersing the oil, told AFP that dispersants "sink the oil into the water column."
"Saying there is no evidence of plumes when you're using dispersant is disingenuous," Pedigo said.
Fish scientist Prosanta Chakrabarty called the BP boss's statement "a disgrace."
"They haven't offered any evidence to counter what at least four independent teams of university researchers have found, and when you look at the difference between what BP said was coming out of the well in the beginning and what really is coming out, you have to question them," he said.
Chakrabarty warned that the oil and dispersant mix that is lurking below the surface of the Gulf could wipe out dozens of species of fish, including two different species of pancake batfish which he discovered six months ago.
"Currently there are no reports about massive fish kills being sighted, but I'm afraid that a lot of damage is being done below the surface where the majority of oil is," he said.
Schweiger said that, with most of the oil hiding deep beneath the sea, "This is much more of a chronic problem than it is dramatic."
"It's a different kind of problem because of the way the oil has been dispersed.
"This is going to be a slow-motion play-out over months and years and will have enormous impact on fisheries and on bird life and on all the things we care about in this region," he said.
Explore further: EU adopts climate change targets for Paris conference (Update)