In the 2 1/2 months since the spill began, the gulf has been examined by an armada of researchers — from federal agencies, universities and non-profit groups.
They have brought back vivid snapshots of a sea under stress: sharks and other deep-water fish suddenly appearing near shore, oil-soaked marshes turning deathly brown, clouds of oil swirling in deep water.
But, with key gaps remaining in their data, there is wide disagreement about the big picture.
Some researchers have concluded that the gulf is being spared an ecological disaster. Others think ecosystems that were already in trouble before the spill are now being pushed toward a brink.
"The distribution of the oil, it's bigger and uglier than we had hoped," said Roger Helm, a U.S. Fish and Wildlife Service official and the lead scientist studying the spill for the Interior Department.
"The possibility of having significant changes in the food chain, over some period of time, is very real. The possibility of marshes disappearing . . . is very real."
Helm said that his prognosis for the spill had worsened in the past week — as the amount of oily shoreline increased from Louisiana to Florida, despite cleanup efforts. "This just outstrips everybody's capability" to clean it up, he said.
The official toll of dead birds is about 1,200, a fraction of the 35,000 discovered after the Exxon Valdez spill in 1989.
But this, too, has been called into question. Officials can only count the birds they can find, and many think a number of oily birds have sought refuge in the marshes.
Other scientists have focused on more subjective measures of the gulf's health — not counting the dead, but studying the behavior of wildlife, the movements of oil and the state of larger ecosystems. For them, solid answers are even more elusive.
Further offshore, federal scientists and university researchers have disagreed about the existence of "plumes" or "clouds" of dissolved or submerged oil.
Several educators have reported finding underwater oil dozens of miles from the spill: Sometimes, they reported it was so well dissolved that the water appeared clear. In other situations, they found what they thought to be oil globs the size of golf balls.
Doug Inkley, senior scientist at the National Wildlife Federation, said he did not think the government had studied these areas well enough yet.
“I've been frustrated with the calm reassurances that we've been receiving, because . . . I don't know what they're based on," Inkley said.
In Sarasota, Fla., scientists found an 11-foot tiger shark, normally an open-water fish, drifting near the surf. That, plus sightings of whale sharks and other creatures outside their normal environmental range, raised concerns that oily water or low oxygen in the central gulf might be driving fish toward land.
"It would be like, to these fish, almost like an island, a huge island rising up in the middle of the gulf," said Bob Hueter of the Mote Marine Laboratory in Sarasota.
Seeing this and other strange patterns in fish, Hueter said, "I just, all of a sudden, just felt this impending sense of doom, that the place that I loved was going to be changed in a very dramatic way."