Touring river-swollen flood areas from Steele Bayou to Grand Gulf by helicopter Friday, Gov. Haley Barbour said he’s optimistic that levees will hold but that residents need to be ready to leave if there is any chance of danger.

“Everybody needs to pray for the best but prepare for the worst,” Barbour said at a news conference Friday at the Vicksburg Municipal Airport.

In some areas, a home might not be flooded but nearby roads could be, hampering the response of fire, police or ambulances.

“Evacuate to save your own life and the life of the people who won’t have to rescue you,” said Barbour, who was to activate National Guard units today to act as military police assisting local law enforcement.

Friday night, the river at Vicksburg was at 55.6 feet, up from 55.5 feet Friday morning. The river is set to crest at 57.5 feet Thursday.

“We expect a long, flat crest of around 57 and 1/2 feet for several days,” said the governor, flanked by state Rep. Alex Monsour, R-Vicksburg, Warren County Supervisor Bill Lauderdale and a number of representatives from FEMA and MEMA. “The backwater areas will be under water for three to four weeks.”

But, “the good news,” he said, “is that the Mississippi River levees are holding.”

Black, high-density polyvinyl layers secured by sandbags have reinforced the Yazoo Backwater Levee and the U.S. Army Corps of Engineers has done all it can to strengthen it as floodwaters have overtopped it in some places by several inches, Barbour said. Occasional sand boils and seepage were being dealt with.

In Vicksburg and in Warren County where low-lying lands have flooded, the governor stressed the need for people to stay out of water that could be contaminated with e-coli and other harmful bacteria.