Rain continued to fall Monday after four days of torrential downpours drove hundreds of New England residents from their homes, washed out roads and forced the governors of New Hampshire, Maine and Massachusetts to declare states of emergency.
And the National Weather Service warned that the worst may be yet to come. Rain totals could hit 15 inches by Monday afternoon, prompting flooding not seen in some areas since 1936.
Massachusetts Gov. Mitt Romney said a burst pipe in Haverhill has allowed about 35 million gallons of sewage per day to flow into the Merrimack River and a treatment plant in Lawrence; a submerged power source was contributing an additional 115 million gallons of sewage to the river.
In Manchester, N.H., the Merrimack River was nearly nine feet over flood level Monday, threatening the millyard, a historic district of brick buildings that was once the world's largest textile complex.
A concrete dam that had been in danger of collapse held firm through the night in Milton, N.H. — a town of about 4,000 people — according to state Office of Emergency Management spokesman Jim Van Dongen. Residents downstream had evacuated, fearing a rushing 10-foot wall of water. The storm has already washed out more than 600 roads throughout the state.
Floodwaters from the overflowing Spicket River blocked Route 28 in Methuen, Mass. Methuen's mayor, Bill Manzi, told FOX News he feared his town "could lose a portion of the downtown to flooding."
Massachusetts emergency management officials predicted more flooding over the next several days, especially in Middlesex and Essex counties, the areas already hardest hit, reported The Boston Globe.
''This is going to get worse before it gets better," said Massachusetts Emergency Management Agency spokesman Peter Judge. ''We're having a hard time anticipating how extensive the damage will be."
Paul Penachio, director of emergency management in Saugus, Mass., told FOX News Monday afternoon that about 70 percent of that town is under water and they are experiencing "major flooding issues" with overflowing reservoirs.
"If it does come over the banks then we're going to have severe flooding and major evacuations," Penachio said, noting that currently "all of the rivers in the town are swollen way above street level."
The governors of Massachusetts and New Hampshire activated the National Guard to aid residents. In Maine, where a state of emergency was declared for York County, schools were closed and a flood watch remained in effect as rain continued to fall.
"It's a very serious situation," said New Hampshire Gov. John Lynch. "It continues to change and the situation continues to worsen."
The state Office of Emergency Management said at least a dozen dams were being closely watched. In Somersworth, N.H., residents were told to conserve and boil their drinking water after the Salmon Falls River overflowed into the city's water-treatment plant.
The Merrimack River, which chased more than 100 people from homes in Manchester, N.H., was expected to rise two more feet before cresting, and the Charles and other large rivers could swamp entire neighborhoods if they spill their banks.
Just north of Massachusetts, fast-rising floodwater forced scores of families to flee homes near the Mousam River in Maine.
Yetta and Steven Chin and their three children awoke early Sunday when firefighters rang their doorbell in Kennebunk, Maine, with a warning. Less than an hour later, the firefighters returned, telling the family they should evacuate immediately: The water in their one-story ranch-style house was chest high by the time they got out.
"We were just an average American family thinking about maybe a summer vacation this year and now we're homeless," Yetta Chin said from the fire station where her family took refuge. "We take turns crying, and we take turns trying to bolster each other."
In York Beach, Maine, kayakers paddled down a main street where yellow police tape blocked off part of the downtown, and firefighters in a boat were going from building to building, making sure that propane tanks were shut off. By late Sunday night, more than 10 inches of rain had fallen in York.
Early Monday in Concord, N.H., the storms broke the previous May rainfall record of 9.52 inches, set in 1984, and the month isn't even half over.
"My back yard is an ocean," said Tom Johnson, of Salem, N.H. "It looks like the beach."
In New Hampshire, more than 600 roads were damaged, destroyed or under water, officials said, and many schools in the southern part of the state were closed.
The flooding was so widespread in the suburbs north of Boston that at least three dozen school systems cancelled classes Monday. Even a stretch of heavily traveled U.S. 1 was shut down as commuters faced a web of detours.
Charley Ranen, one of about 300 people evacuated from a senior citizens' apartment complex in downtown Peabody took shelter at a high school.
Deb Gaudette and her family were among about 50 families that had to evacuate from Goffstown, N.H. She admitted she was having a tough Mother's Day, "but I have my kids, that's all I need," she said.
The Associated Press contributed to this report.