A natural gas explosion sunk the Deepwater Horizon oil rig in the Gulf of Mexico in April 2010. The accident killed 11 rig workers and oil spilled into the sea for much of the summer.
The National Wildlife Federation, in a report on the regional ecosystem, said many complications from the spill are developing.
Doug Inkley, a senior scientist at the NWF, explained that the impact of oil disasters like the 1989 grounding of the Exxon Valdez off the coast of Alaska can last for decades.
"Little action has been taken to address the long-term species threats and wetlands habitat degradation exacerbated by the oil disaster," he said in a statement.
The NWF report said dolphin, coral and other aquatic species were dealt a "severe blow" by the oil disaster.
NWF scientists added there were "unknown" effects at coastal areas in and around the Mississippi River Delta. Those areas were losing about 45,000 square feet of land every hour to the effects of the oil spill.
"Much more needs to be done to ensure a complete recovery," said Inkley.