Schools were canceled for a second day and thousands of residents remained stranded from their homes as a weakened dam again threatened to give way and send a wall of water through this southeastern Massachusetts city.

Mayor Robert G. Nunes (search) said Tuesday that crews were working to relieve pressure from the 173-year-old Whittenton Pond Dam (search), which buckled earlier in the week under heavy rain. The mayor said the situation was under control, but "extremely volatile."

"This is minute-by-minute," he said of the situation in this working-class community 40 miles south of Boston.

At a news briefing Wednesday morning, Nunes said that while the city remains in a state of emergency and there still is a significant amount of water behind the dam, "However, we are winning."

He said he could not say how long the state of emergency would continue.

"We're erring on the side of caution," Nunes said. "We don't want to jump and say everything is OK, and, God forbid, have something happen."

Matt Bellisle, engineer hired by the owner of the dam, Jefferson Development of Leominster, said that while the water behind the dam continues to recede, the water remains several feet above normal levels. He said no major changes occurred overnight at the dam.

Despite reports Tuesday that excessive vibrations at the dam had officials concerned, Bellisle said "excessive" may be too strong.

"The vibrations that are out there are not a concern at this point," Bellisle said, adding that wood dams vibrate to release some of the stress in the structure.

Crews have opened floodgates on the wooden dam, and also adjusted the flow on a second dam upstream. National Guard troops have placed sandbags upstream in an effort to slow down the flow of the rain-swollen Mill River.

"Both dams are performing as they should," said Fire Chief Joseph Rose. "But there is still a substantial amount of pressure on them."

Since the beginning of the month, Taunton has received 111/2 inches of rain, including more than 7 inches from Friday through Sunday.

The mayor on Monday ordered about 2,000 residents who live near the Mill River to evacuate. Though the rain has stopped, the situation at the dam worsened after some of the dam's timbers washed away.

Dive teams were standing by in case rescues proved necessary.

Nunes said businesses in the downtown area, along with all government offices and state courts, would remain closed Wednesday.

Officials said Tuesday night that the water-level in Lake Sabbatia (search), the body of water behind the dam, had receded slightly and was stabilizing. A sandbagging operation at the dam continued throughout the night in an effort to ease pressure on the structure.

"We're very happy with stable water," the fire chief said. "However, we're not convinced we're out of the woods yet."

Officials fear that a break in the dam could send 6 feet of water surging through downtown Taunton, flooding businesses and destroying homes. They also worry that if Whittenton Pond Dam collapses, so could the Morey's Bridge dam upstream, because it no longer would have counteracting pressure on its downstream side.

Nunes canceled school on Tuesday, and said the closure would continue on Wednesday.

The city center on Tuesday was empty as stores were also closed and police barricaded nearby streets. Highways in the area were closed down.

"I understand," said Brian Bishop, who has a curtain and bedding store on Main Street. "It's better to be safe than sorry. I've got a lot of money to lose if this thing goes and water comes tearing down the street."

Wednesday morning, city officials planned to tour the dam site with Sens. Edward M. Kennedy (search) and John F. Kerry (search), Rep. Barney Frank (search) and Gov. Mitt Romney (search).

Whittenton Pond Dam is one of about 3,000 private dams in the state. It was inspected two years ago and was considered in fair condition at that time, Romney said.

One of the owners, Steve Poelaert, said Tuesday night that work to restore the dam was to have begun last Friday, but was delayed because of heavy rain.

On Tuesday, Romney ordered the emergency inspection of all high-risk dams in the state. Dams are considered high risk when, "if they were to breach, there would be a significant loss of life or property," he said.

The 12-foot-high Whittenton Pond Dam dates to 1832, and is near homes and businesses about a half-mile upstream from downtown Taunton. It was built to power a textile mill, but no longer has any industrial purpose.

The city last flooded in 1968, when the same dam broke.