Brattleboro, Vermont (CNN) -- As a much-weakened Irene entered Canada, it left behind parts of the U.S. East Coast still grappling Monday with dangerous flood waters, widespread power outages and stranded residents.
At least 21 deaths in nine states were blamed on Irene, which fizzled to a post-tropical cyclone and headed over eastern Canada on Monday.
"Hurricane Irene's damage is likely to be characterized more by the amount of inland flooding, storm surge and treefall than by direct wind damage, and flooding is still an ongoing concern for many states in the Northeast," said Risk Management Solutions, Inc., which tracks natural catastrophes.
About 3 million customers were without power along Irene's path.
Much of the remaining trouble centered on flooding from North Carolina through New England, with homes inundated and roads torn apart by floodwaters.
Some of the worst flooding since 1927 ravaged Vermont's normally tranquil countryside, turning babbling brooks into turbulent rivers and knocking homes from their foundations.
In Wilmington, Vermont, a young woman who had been standing near a river was washed away. Her body was recovered.
In all, 260 roads were affected, many of them underwater, Vermont's Emergency Management Department said Monday.
Four to six covered bridges were destroyed and others were washed out, it said.
In the capital city of Montpelier, water crested overnight at 19.5 feet, just shy of the 20-foot prediction, but levels throughout the state were receding Monday morning.
The emergency management headquarters flooded overnight and was evacuated and relocated from Waterbury to Burlington, approximately 20 miles away.
In North Carolina, more than 340,000 customers were without power Monday, down from more than 440,000 on Sunday night, the state's emergency management department said.
Dominion Power reported more than 600,000 customers were without power in Virginia and northern North Carolina.
As many as 200 residents were isolated and without power Monday on Ocracoke Island, near where Irene had first made landfall as a hurricane on Saturday. Supply transport to Ocracoke was hampered as ocean waves dislodged large chunks of a key roadway.
Dunes at Ocracoke's northern end "have apparently been spread across the road, so no one yet knows how badly the pavement is damaged," said Clayton Gaskill, manager of Ocracoke's tiny FM radio station WOVV.
And in Prattsville, New York, seven Brooklyn families who thought they had escaped the storm's wrath were stranded Monday in the Catskill Mountains after bridges crumbled around them.
"We're sitting in one room, and it's a horrible situation and there is no way out," said Irina Noveck, who was stuck along with 22 other adults and children. "Kids are getting scared, food is getting spoiled."
In all, more than 8,500 people awoke Monday morning in Red Cross shelters up and down the East Coast, a spokesman said.