It's hard to sense how vast this problem is, until you see it from the air. A group of government officials has just buckled up their life jackets, because they're going to see the crisis first-hand.

One official has just flown in from the Pentagon, a few come from the state capital of Louisiana. And now this bright yellow helicopter lifts off the banks of the Mississippi River, and it heads toward a landscape that's vanishing. Guiding this inspection is biologist Bill Good who works with the state's department of natural resources. He says every couple of years, Louisiana loses a chunk of land that is bigger than Manhattan.

"And," Good notes, "if a foreign country came in and took that much of our real estate every year, that would be grounds for war."

The helicopter heads south along the muddy Mississippi. We skirt the skyline of New Orleans. We buzz over oil refineries and shipyards and freighters loaded with grain. Suddenly, civilization seems to come to an end.

We're flying over Louisiana's wetlands. Coastal wetlands are lands that get flooded by tides. They're bursting with life, like rainforests , and these are some of the greatest wetlands on Earth. They sprawl 300 miles along the Gulf of Mexico, and they go up to 50 miles inland. They're the heart of the Mississippi Delta; and this astonishing landscape is vanishing. Good says if we'd taken this helicopter trip 50 years ago, it would have looked like the Great Plains.

"Exactly. It would look just like the prairies in the Midwest," says Good. "They were very solid, vast expanses of grass, of beautiful area, of verdant green from horizon to horizon."

Next: A Tragedy of Immense Proportions