Even as relief efforts continue for the victims of Hurricane Katrina, attention is turning in some quarters to the immense task of cleaning up ravaged areas. New Orleans was overrun with dirty water contaminated by waste and chemicals. The environmental impact of Katrina is likely to be severe.

Hurricanes usually leave some imprint on the environment long after they dissipate, such as eroded beaches and flattened trees. But experts say Katrina's environmental damage puts her in a class by herself.

Hugh Kaufman, senior policy analyst at the U.S. Environmental Protection Agency, said the clean-up costs are likely to be staggering. "You're talking about a potential commitment almost to the level of the financial commitment we're putting into Iraq in terms of resources for evacuation, helping people rebuild, and remediation (of environment). This is a substantial hit that will hit both the taxpayers and the insurance companies," he said.

The breaches of the levees that were supposed to protect New Orleans sent millions of liters of water cascading through the streets, putting some 80 percent of the city under water.

Mr. Kaufman of the EPA, who has dealt with environmental emergency response for some 35 years, said that water is thoroughly contaminated. "Remember, you've got landfills down there, hazardous material storage areas, industrial wastewater, all of which has contaminated the whole area. It's basically a horrific situation for everyone down there, and for the whole country economically," he said.

That water will have to be eventually pumped out of New Orleans. But where? Back into the Gulf of Mexico, say experts.

As Ken Green, executive director of the Environmental Literacy Council, explains, there is simply no other option except to send the untreated water back into the Gulf. "They have had a lot of sewage and a lot of chemicals that has hit the water, and there's really no way to treat that amount of water that they're going to have to pump out of the entire city. And, so, it's going to be dumped straight into the Gulf [of Mexico], which means you're going to have higher concentrations of those kinds of toxins in the Gulf waters. As I said, the scale of the disaster is such that you can't run this water through a treatment system to purify it before you put it out in the ocean," he said.

He says time will eventually heal most of the environmental damage to the Gulf of Mexico. But there is concern about how dumping the contaminated water might affect the fishing industry.

Asked about the impact of the storm on the industry, Walter Keithly, a seafood economist at Louisiana State University, says it is considerable, but not from environmental pollution. "It's going to be very, very large and long-term. But the reason is not necessarily due to contaminated waters as much as just a complete destruction of the infrastructure in the central Gulf here," he said.

The Gulf of Mexico is rich in oysters and shrimp. However, according to industry statistics, 90 percent of the shrimp consumed in the United States is imported, primarily from Southeast Asia.