Katrina Takes Environmental Toll

"It is almost unimaginable what we're going to have to plan for and deal with," said Mike McDaniel, the state's secretary of environmental quality. "I don't think anyone has ever dealt with this. The tsunami comes to mind."

When residents return to the city, they will probably need to bring in bottled water and other sources of water while the city rebuilds water-treatment plants.

The mix of contaminants poses a serious disease risk to those wading through the filthy water on rescue and body-recovery missions, McDaniel and others warned. Rescuers were urged to get hepatitis and tetanus shots.

In a telephone news briefing Tuesday, Julie L. Gerberding, director of the Centers for Disease Control and Prevention, said "it would not be too surprising" if evacuees living in shelters experience somewhat higher rates of infectious illness.

Respiratory illnesses, including influenza when the season for it begins in the fall, are the most likely, she said. Diarrheal diseases are also possible, especially ones caused by norovirus and the bacterium Escherichia coli . The infections most likely to appear are ones already in the population before the flood, she said, noting that "in the city of New Orleans, cholera has not been present for years."

Other aspects of the environmental toll wrought by Katrina are obvious to rescuers and others traveling the increasingly empty city. On such grand boulevards as St. Charles and Napoleon avenues, the foliage that drapes the majestic oaks and magnolia trees is suddenly turning brown. Birdsong has largely disappeared, replaced with the whine of boat engines and the shouts of rescuers seeking survivors.

Lloyd Thornton, a volunteer from Kemah, Tex., cut the engine on his airboat Tuesday while floating along General Taylor Street. He and his companion, a New Orleans police officer, spotted a towel hanging out a broken window that could have been a cry for help.

"Is anybody in there?" Thornton yelled. "Is anybody home?"

There was no answer. Thornton restarted the engine and continued the search.

Salmon reported from Baton Rouge, La.; Eggen, from Washington. Staff writers David Brown, Juliet Eilperin, Michael A. Fletcher, Spencer S. Hsu and Shankar Vedantam and research editor Lucy Shackelford contributed to this report from Washington.