Louisiana state officials say the flooding of New Orleans has created environmental problems that may take years to correct.
The state's top environmental official, Mike McDaniel, told reporters on Tuesday that Hurricane Katrina has left the city with "almost unimaginable" problems.
Concern is centered on the floodwaters contaminated from raw sewage, debris, and other hazardous substances.
The water has been further tainted by two oil spills from local storage facilities. The U.S. Environmental Protection Agency has warned people to limit contact with the water due to the risk of illness.
Some experts have expressed concern that the water may kill fish and destroy ecosystems as engineers pump it back into Lake Pontchartrain and the Mississippi River.
But Mr. McDaniel remains hopeful for the long-term, saying nature is resilient and is likely to recover.