This National Geographic video shows how the levees of New Orleans contributed to the destruction of the city's natural protection against violent storms. Scroll below the video player to read more.

August 31, 2005—One acre (about half a hectare) of wetlands along Louisiana's shoreline is being lost every 25 minutes, according to one estimate.

The erosion of vegetation is also the loss of New Orleans's last line of defense against hurricanes, such as the devastating Category Four Hurricane Katrina, which struck the Gulf Coast this week.

New Orleans is below sea level and is surrounded by water: Lake Pontchartrain, the Mississippi River, and the Gulf of Mexico. Levees were built around the city to protect it from flooding when surrounding water levels rise.

In this National Geographic video filmed in 2001 you will see how New Orleans's levees contributed to the loss of the extensive wetlands of the Mississippi River delta. Wetlands are natural barriers to storm surges.

—David Braun

See more about this in U.S. Oil, Gas Threatened by Louisiana Wetlands Loss

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