NEW ORLEANS (AP) - The floodwaters that caused so much misery and death in New Orleans were being pumped back into Lake Pontchartrain and authorities braced for what the receding deluge would reveal. ''It's going to wake the nation up again,'' Mayor Ray Nagin said today.

The U.S. Army Corps of Engineers began pumping water out the flooded city after closing a major gap in a key levee that burst during Hurricane Katrina, flooding 80 percent of the bowl-shaped city.

Nagin said it would take three weeks to clear the water and another few weeks to clear debris. It could also take up to eight weeks to get electricity back on.

''I've gone from anger to despair to seeing us turn the corner,'' Nagin said Tuesday on NBC's ''Today.'' He warned that what awaits authorities below the toxic muck would be gruesome. ''It's going to be awful and it's going to wake the nation up again.''

Efforts to evacuate holdouts were stepping up Monday, with boat rescue crews and a caravan of law enforcement vehicles from around the country searching for people to rescue.

''In some cases, it's real easy. They're sitting on the porch with their bags packed,'' said Joe Youdell of the Kentucky Air National Guard. ''But some don't want to leave and we can't force them.''

In neighboring St. Bernard Parish, officials expressed frustration that federal aid, slow to reach New Orleans, was even slower to get to outlying areas.

''This is Day 8, guys. Everything was diverted first to New Orleans, we understand that. But do you realize we got 18 to 20 feet of water from the storm, and we've still got 7 to 8 feet of water?'' said Ron Silva, a district fire chief. ''If you had dropped a bomb on this place, it couldn't be any worse than this.''

A Canadian task force of firefighters and police arrived four days after the storm to help, St. Bernard Fire Chief Thomas Stone said.

''If you can get a Canadian team here in four days, U.S. teams should be here faster than that,'' Stone said. Pointing to two large oil refineries, ''When they're paying $5 to $6 a gallon for gas, they're going to realize what this place means to America.''