Pounding rains and rising waters likely killed three people, flooded hundreds of homes, swept away a historic covered bridge, closed dozens of roads and caused millions of dollars of property damage in the worst storm here since Tropical Storm Agnes in 1972.

The northwestern part of the county was hammered Wednesday and Thursday by a storm system that has been parked over the county since Monday, dumping anywhere from 7 to 15 inches of rain here. Rain-swollen streams have spilled over their banks, causing flooding throughout the northern part of the county.

The Susquehanna River continues to rise, causing residents of Marietta to frantically move belongings out of homes or to higher stories during a mandatory evacuation.

The Pennsylvania National Guard sent troops to the county to help with evacuations and ferry emergency workers as storm-weary residents faced their fourth day of rain.

Most of the county's schools closed Thursday, as did the county courthouse, Elizabethtown College, Millersville University and Harrisburg Area Community College.

Donegal and Elizabethtown school districts announced their schools also will be closed today. Manheim Central, Lancaster Mennonite, Lancaster Catholic, Cocalico, Conestoga Valley, Hempfield, Warwick and Ephrata announced two-hour delays. More closures and delays likely will be announced in the early morning hours, said Phil Colvin, deputy director of the Lancaster County Emergency Management Agency.

Elizabethtown College announced that classes will resume this morning.

Storm-related cancellations and postponements of weekend events also were announced.

"It's a very significant event," said county emergency management coordinator Randy Gockley. "No doubt about it, the damage will be in the tens of millions of dollars for Lancaster County."

The county likely will seek federal disaster aid once it can assess the amount of damage, he said.

Gov. Tom Corbett sent a letter Thursday afternoon to President Barack Obama asking for federal disaster assistance. Members of the state's congressional delegation were expected to follow with their own letter to the president.

The deaths occurred when people were caught in the rising waters.

• A 62-year-old woman in a vehicle became stranded on Route 322 near Pumping Station Road in Elizabeth Township Thursday morning. Her car was swept away in the water and submerged. Her death likely will be attributed to drowning, the county coroner said.

• An 8-year-old boy playing in a flooded backyard in East Cocalico Township Thursday afternoon was swept off his feet by the water. His head became caught in a submerged storm drain, where he was found by emergency personnel. He was taken to Ephrata Community Hospital, where he was pronounced dead.

• A man was swept away as he tried to walk through water just off White Oak Road, near the border of Rapho and Penn townships. His body had not been recovered late Thursday and he is presumed to be the third person killed by the storm.

Lancaster County's emergency dispatchers handled 1,600 calls for assistance between midnight and 4 p.m. Thursday.

Conditions improved as the day went on, with streams cresting, roads reopening and people starting to face the overwhelming cleanup in front of them. The rain tapered off as well.

Many dramatic rescues took place during the storm and in its aftermath.

In West Hempfield Township, a crew in boats helped a couple evacuate their home near Siegrist and Farmdale roads.

In Manheim, crews manned about 10 boats to take people from their homes in the darkness of the early morning as water filled the streets in the southern end of the borough.

About 30 people gathered early Thursday at a shelter set up at Manheim Central Middle School.

One of them, John Carloni, 45, said water filled the basement and first floor of his South Main Street home.

"I tried to grab what I could to take to the second floor," he said. "Everybody outside was screaming, 'Call 911!' You could hear the panic and fear."

The Manheim shelter was later closed. Evacuated residents were directed to a Red Cross emergency shelter at Donegal Middle School, 1175 River Road, Marietta.

About 20 people were at the shelter by late afternoon, said Stu Metzler of the Salvation Army in Lancaster. The Salvation Army had taken food to the shelter to supplement the efforts of the Red Cross, Metzler said.

Kathy Smyser, of the American Red Cross, said Thursday night that there were 13 people at the Marietta shelter who planned to stay the night. Another 10 had come for dinner and then left to stay with family and friends, she said.

The Marietta shelter replaced one in a smaller space at Columbia Consolidated Fire Company.

In Ephrata, Ephrata Middle School was used as a shelter before being closed in the evening.

Lancaster County Animal Rescue will be coordinating shelters for pets, the Red Cross reported.

A dozen boroughs and townships declared disaster emergencies and have urged residents to stay off roads and restrict water usage.

Emergency crews on a regular basis rescued people from houses and vehicles in many areas overnight and early Thursday.

Streams, creeks and rivers overflowed their banks all over the county.

The rushing waters of Chiques Creek swept away the Siegrist's Mill covered bridge on Siegrist Road late Thursday morning, pushing it downstream, said Lancaster County Commissioner Scott Martin.

Built in 1885, it weighed five tons and straddled the border between West Hempfield and Rapho townships, Martin said. The county owns the bridge.

Kelly Williams of Rapho Township lives near the bridge and happened to be shooting photos. He shot a video of the bridge when it was swept away.

Williams said two women who were watching the bridge said they heard snapping sounds.

"It was pretty slow," he said. "It leaned more and more and then just sort of broke away."

During Agnes, the bridge shifted a few feet and was cemented back into place, neighbors told Williams.

Martin said officials were keeping a wary eye on the Route 462 bridge over the Conestoga River at Bridgeport. The river had almost reached the bridge when it crested Thursday afternoon. The bridge was reopened to traffic after the river receded, Colvin said.

Other problems cropped up along the Conestoga.

Lancaster city officials Thursday evacuated residents from low-lying areas of Almanac Avenue and South Broad Street, near the river.

Crews also evacuated 25 people from Conestoga Boulevard in Conestoga Township, going door to door to ask them to leave their homes, Gockley said.

The Conestoga River crested at 21.3 feet at 12:30 p.m. That level is more than 10 feet above flood stage and is second only to the level of 27.9 feet it reached when Agnes hit in 1972.

Hundreds of roads were closed across the county, a county dispatch supervisor said. Parts of major routes were closed, including routes 222, 30, 23, 72, 441, 230, 322, 741 and 772.

The state Department of Transportation reported that 28 roads in the county remained closed as of 10:30 p.m. Thursday.

A 39-mile section of the Pennsylvania Turnpike between Reading and Harrisburg also was closed during evening rush hour. The closure was done in response to the Swatara Creek, which is bridged by the turnpike.

"Anywhere a stream crosses a road in the northwestern part of the county, the road is closed," Gockley said.

Cocalico Creek in Ephrata Township and Chickies Creek in Rapho Township both crested by late afternoon.

"Some roads will open up; others will continue to be impassable," Gockley said.

Forecasters were calling for rain to taper off Thursday night. Another half-inch to an inch of rain was expected to fall, according to meteorologists at the Millersville University Weather Center.

Four-day rainfall totals as of mid-morning Thursday ranged from 7.76 inches at Lancaster County Central Park, just south of the city, to as much as 15 inches in the Elizabethtown and Mount Joy area.

Those totals compare to the 10.27 inches of rain dumped on the Lancaster city area over three days in June 1972 when Tropical Storm Agnes ravaged the area.

That storm was blamed for the deaths of 10 people and $10 million in damage. That amount would be $54 million in today's dollars.

Other places in the county still have not seen the worst, including Marietta, which was bracing for the Susquehanna River to crest at 62.2 feet early Saturday, its highest peak since Agnes, when it peaked at 64.5 feet. Flood stage is 49 feet, which was reached Wednesday at 9 p.m.

Emergency officials ordered residents of Front Street and Hazel Avenue in Marietta to evacuate by 5 p.m. Thursday.

All utilities were shut off in that area, and a curfew was in effect, barring people from those streets until this morning.

At McCleary's Pub on West Front Street, more than a dozen people helped to move everything out of the restaurant and bar and into waiting trucks on Thursday.

Owner Gene Pelland said, "I gotta tell you I am overwhelmed at the level of support that has just showed up. I don't even know half of these people's names."

A few doors down, Gerry and Annie Rice were moving appliances and moved other belongings to the second floor of their home.

Storms have come and gone over the years, but the Rices said they had not evacuated since Agnes, when the water rose to the middle of their first floor.

But they weren't staying Thursday.

"It's just too much," Rice said. "This time, we have to move."

Downstream, PPL ordered the evacuation of its Holtwood Hydroelectric Plant on Thursday afternoon. The generating plant was shut down and about 20 plant employees were evacuated, beginning about 4 p.m. Another 80 workers involved in the ongoing $434 million expansion of the plant also were evacuated.

The last time the hydroelectric plant went through an emergency shutdown and was evacuated was probably during Agnes, a PPL spokesman said.

Staff writer Ryan Robinson contributed to this report.

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