On April 29, a mere nine days after the rig explosion, the Gulf's so-called Loop Current was at full strength, says Murawski, chief fisheries scientist for the National Oceanic and Atmospheric Administration. Under those conditions, it had the potential to take any oil that got into its pinwheel-like effect and spin it into the Florida Keys and up the U.S. East Coast.
Then, just days later, a large eddy blocked the current and broke the Loop's back. The threat disappeared.
"This is the closest thing to an act of God that we've seen," says Murawski.
As the oil continued to gush, scientists and others feared a near-knockout blow to the Gulf's already stressed ecosystem. Early signs suggest that didn't happen.
In parts of Louisiana, some marshlands seem already to be recovering. The oil-munching microbes that scientists feared would create dead zones ultimately failed to reduce oxygen levels as severely as predicted.
Yes, oil continues to wash up in places, but the streaky surface sheens have all but vanished. And while nearly 6,600 dead birds, sea turtles and other animals were recovered, new victims are rarely found.
"I think the resiliency of the Gulf has been endorsed and exceeded even optimistic estimates," says George Crozier, director of the Dauphin Island Sea Lab in Alabama.
But underwater, things get a bit murkier.
Scientists have found plumes of oil — microscopic and unseen — below the surface. A University of Georgia expedition this month found patches of oil, some up to 2 inches thick, on the Gulf floor.
That's oil that can be brought back to the surface and onshore with a storm, says University of South Florida chemical oceanographer David Hollander.
Hollander has found plankton, the base of the marine food web, that bear the hallmarks of having been poisoned. He worries about what that means for fish larvae and eggs — future generations of sea life.
An August federal report declared that all but about 52.7 million gallons of BP's oil had been burned, skimmed, chemically dispersed, naturally dispersed, evaporated or dissolved. Scientists roundly criticized that report as too rosy.
Things are as positive as they are, Hollander and others say, because we were lucky AND smart.
In addition to the fortunate change in the Loop Current, wind patterns kept the oil from spreading and staying close to the shore in Mississippi, Alabama and Florida, says Murawski. Of course, those states' fortune was Louisiana's misfortune.
Credit also goes to those who decided to use massive amounts of chemical dispersants deep underwater to break up the oil. Some say we traded certain slicks for unknown problems below the surface, but Crozier and other initial opponents now concede that it seems to have been the right move.
But the effects of the 1989 Exxon Valdez oil spill in Alaska and the 1979 Ixtoc disaster off Mexico's Yucatan Peninsula are still unfolding, so only time will tell.