The NOAA has recorded that 22 Dolphins have been recorded washed up dead.
From CNN (emphasis added):
Dolphins have washed up dead. Endangered sea turtles have been found with oil stuck on their corneas. Lifeless brown pelicans, classified as endangered until recently, have been carried away in plastic bags. Beaches in Grand Isle, Louisiana, are spattered with gobs of sticky crude. And when the moon rises over the coast there, the oil-soaked ocean sparkles like cellophane under a spotlight.
If scientists' worst fears are realized, the oil plume in the Gulf could choke off and kill coastal marshes in the productive Mississippi Delta and barrier islands, turning these verdant tufts of life -- which look like hairy putting greens floating out on the water -- into open ocean. That would snap the region's marine food chain, exposing and starving all kinds of organisms.
Equally frightening, the oil also could spawn a massive oxygen-free "dead zone" deep in the Gulf's waters, which would suffocate all marine life on the ocean floor. Samantha Joye, an oceanographer at the University of Georgia, said that if that happens, the dead zone could change marine chemistry in the Gulf of Mexico forever.
Despite being told repeatedly NOT to use their chemical dispersant, chemicals that have been banned in England (BP's home country) due to their toxicity, BP has continued to use it anyways, causing the oil to break up and fall beneath the surface, where it cannot be retrieved. It hides the problem from public scrutiny, but doesn't actually fix anything. In fact it makes things worse. And we have no clue how bad things are going to get. Again from that same CNN article:
Researchers know almost nothing about what the oil and chemical dispersants used to try to break up the oil will have on life below the Gulf's greasy surface, Joye said on her boat in Gulfport, Mississippi, just before heading out toward the epicenter of the spill.
"I don't think we know what's going on yet, and it's a month into this thing," she said.
Bacteria eat oil and in the process also chew oxygen out of the ocean. There's so much oil in the water, the bacteria may deplete oxygen reserves until deep-water fish like grouper and snapper and "benthic" communities of sea tubes and oysters suffocate, she said.
BP has released more than 28,000 gallons of chemicals on the ocean, according to the U.S. Environmental Protection Agency, in hopes these "dispersants" will break up the oil and minimize its impact on the environment. Such a huge amount of dispersant has never been released deep into the ocean before, according to the EPA, and some independent researchers and the EPA have questioned whether those chemicals may be making matters worse.
I highly reccomend that you read the entire article, which is found here.