"This spill will be lasting for years if not decades," said Doug Inkley, senior scientist at the National Wildlife Federation. Some of the immediate effects of a spill are obvious -- witness the gut-wrenching images of soaked and suffocating seabirds in the gulf.
But some types of ecological damage are hard to measure and can take years to document. Many of the creatures that die will sink to the bottom, making mortality estimates difficult. Damage to the reproduction rate in sea turtles may take years to play out.
The Exxon Valdez spill of 11 million gallons killed as many as 700,000 sea birds and 5,000 sea otters initially, but even 21 years later, populations of sea otters in areas of Prince William Sound haven't recovered. The Pacific herring population collapsed after the spill for reasons that remain in dispute among scientists.
Two intensely studied pods of killer whales in the sound suffered heavy losses in the spill and have struggled since. One of the two pods has no more reproductive females. It is doomed to extinction.
And the oil? "It's still sitting there," said Stan Rice, program manager for habitat studies at the National Oceanographic and Atmospheric Administration's Auke Bay Fisheries Lab. "It's still liquid, you can still smell it and touch it."