Rescue efforts continue along a large area of the Gulf of Mexico devastated by Hurricane Katrina. Louisiana's Governor has ordered the complete evacuation of New Orleans and, given the rising death toll and preliminary assessments of damage, federal officials say this could be the worst disaster in U.S. history.

It may be weeks before authorities can even come close to stating the total death toll from Katrina. Rescue workers in the worst hit areas of Mississippi and Louisiana say they have seen dead bodies floating amid debris, but they generally do not try to retrieve them, concentrating instead on helping survivors, many of whom are stranded on roof tops or in the upper stories of buildings with no food, no clean water and no medical supplies.

After levees gave way in New Orleans Tuesday, 80 percent of the city was inundated. Louisiana Governor Kathleen Blanco called for the full evacuation of the city, much of which lies below sea level and relies on a system of levees, dikes and pumping stations to remain dry under normal conditions.