In the wake of the Katrina disaster in New Orleans, the US Army Corps of Engineers has increased its investigations of the safety of thousands of levees around the country. On Feb. 1, 2007 - on the heels of a FOIA request by USA TODAY - the Corps released a list of 122 levees  that have been poorly maintained and could readily fail. Additional defective levees could be identified in the near future (release ).
The known defective levees are in 27 states, Washington, DC, and Puerto Rico, and often are in or near sizable cities (for example, in CA, CT, DC, GA, MA, NM, VA, and WA).
Levee owners have been notified of their risky structures, and have one year to fix problems. If the problems aren't fixed, the levees could fail, threatening many people and properties, and the damaged areas may not be eligible for federal assistance. In addition, property owners who could be inundated would at least be required to buy flood insurance, if it's available.
For more details, check with the appropriate Corps District.