BELLE CHASSE, La. – Ever since the Mississippi River laid down this spit of silt and swamp grass, wind and water have conspired to drag it into the sea. And for almost as long, the oystermen, river pilots and others who call it home have refused to let go.

But in Isaac, the residents of Plaquemines Parish are battling an adversary some fear they may have underestimated, even as it weakens to a tropical storm.

“We’ve never seen it this bad – the way this wind is shifting,” said Alvin Sylve, a 52-year-old disabled truck driver, preparing to evacuate from a street of double- and single-wide trailers in Jesuit Bend, an area of Plaquemines outside the federal levee system.

“This double-wide is shaking, even though it’s anchored down. You see another piece came off the roof,” he said inside a friend’s trailer. “It’s falling apart!”

As water spilled over the top of a critical levee Wednesday, this thinly populated parish south of New Orleans was already inundated by Isaac’s punishing downpour, stranding some residents in their homes and forcing more to flee.

“We didn’t think it was going to be like that,” electrician Joshua Brockhaus said after rescuing flood-stranded neighbors in his boat. “The storm stayed over the top of us. For Katrina, we got 8 inches of water. Now we have 13 feet.”

Officials braced for the worse and said they would cut a hole in a levee in the parish to relieve pressure on the structure, though they did not say when. They also had to wait for the winds to calm before they could begin search-and-rescue efforts.

“We’re going to get out there to them. We’re going to do everything we can to get them out of there. But we’re not going to put further people in harm’s way,” said Col. Mike Edmonson, superintendent of the Louisiana State Police.

The Louisiana National Guard brought in 14 high-water vehicles and 10 boats, and as many as 70 people were rescued from homes with water up to their roofs in some places. Officials believed no one else was stranded.

Plaquemines, a mostly rural fishing and farming community threaded by the Mississippi and known for its rough and tumble residents, is proud of its ability to withstand and recover after hurricanes. But it has always been a tenuous struggle on this perilously exposed ribbon of earth, a place nearly entirely below sea level. It’s as much water as it is land.