Senators are worried that repairs to New Orleans' levees may not offer enough protection against another tropical storm.
Engineers have told a Senate panel that dozens of breaches continue to mar the levee system, including a large seep at the Industrial Canal last week.
They say the initial rebuilding process was done with little or no engineering guidance and perhaps substandard materials.
Republican Senator Susan Collins calls the findings troubling.
Democrat Joe Lieberman questions whether the levees could protect New Orleans from high tides, let alone another hurricane.