This is a partial transcript of "The Big Story With John Gibson," September 7, 2005, that has been edited for clarity.

JOHN GIBSON, HOST: Keeping an eye on New Orleans. As you can see, the Coast Guard is still working rescue helicopters over New Orleans. The feds say New Orleans's floodwaters are even too polluted to touch, filled with sewage, bacteria that's at least 10 times higher than acceptable, safe levels.

So is it risky to pump this contaminated water back into Lake Pontchartrain (search)?

As we keep an eye on these pictures in New Orleans, the Coast Guard helicopter carrying a sling and water bucket. The New Orleans firefighters fighting both fires and floods at the moment.

But joining me on the phone is Frank Manheim, a former geochemist for the U.S. Geological Survey and a professor at George Mason University. He also co-authored a report on pollution in Lake Pontchartrain. So Mr. Manheim, you've seen this water being pumped out of the streets of New Orleans — which has been described as a toxic stew — into Lake Pontchartrain. Does that just sound bad? Or is it in fact really bad?

FRANK MANHEIM, GEORGE MASON UNIVERSITY: No, it's worse for the people in New Orleans because for them, it's directly toxic, and infection is a bad deal. And then, of course, you have huge amounts of oil, from the reports I've been hearing.

Although one report appears to have been exaggerated. There was an early report that really scared me. It said 78,000 barrels of oil had supposedly been released into Pontchartrain. It turns out from the Louisiana Department of Environmental Quality that that isn't the case.

GIBSON: OK, let's talk about what is the case.

MANHEIM: Well, we don't know the exact measurements. Because as I understand it, the Environmental Protection Agency (search), together with the Louisiana Department of Natural Resources, is sampling as we speak. And some of the early evaluations are what you just reported.

GIBSON: Right. But who should be worried? People, you know, in between New Orleans and the ocean or the Gulf, who will eventually see this water come their way? People who live alongside Lake Pontchartrain? People in New Orleans? Who?

MANHEIM: Well, of course, the people in New Orleans — I'm hoping there are fewer and fewer that are still there — are suffering from the most atrocious conditions. Those who survived and had little to go back to, and the health conditions right now are terrible.

When you move to Lake Pontchartrain, it's quite a different and more complex story. You have to remember, Lake Pontchartrain is a place of 630 square kilometers, square miles.

GIBSON: Frank Manheim, former geochemist, sorry, I've got to go. Appreciate it. Thanks a lot for the information.

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