(CNN) The rains may have stopped in South Carolina, but the danger and the work to rebuild are far from over.

"I believe that things will get worse before they get better," Columbia Mayor Steve Benjamin told reporters Monday.

"Eventually the floods will abate, but then we have to access the damage, and I anticipate that damage will probably be in the billions of dollars, and we're going to have to work to rebuild. Some peoples' lives as they know them will never be the same," he said.

One of those people is Columbia resident Angela Williams, who watched the relentless rainfall destroy her neighborhood.

"We have lost everything. What I got on my body is what we have," she told CNN affiliate WIS-TV . "Pretty much everybody down that hill there has lost everything ... our vehicles, our clothes, everything.

"But the best thing is that we still have our lives."

Eleven people are known dead in the state due to weather-related incidents. Of those, seven drowned, according to the South Carolina Department of Public Safety. Four others died in traffic accidents.

One of the deaths was a state transportation employee.

Timothy Wayne Gibson, 45, died Sunday in floodwaters while overseeing work in Columbia, the South Carolina Department of Transportation said.

North Carolina reported two storm-related deaths. Both were the result of motor vehicle accidents, in Cumberland and Jackson Counties, according to Julia Jarema, an emergency management spokeswoman.

South Carolina Gov. Nikki Haley warned there could be other deaths.

BREAKING: A pastor from a church in Summerville pulls an unearthed casket out of the flood waters in Ridgeville pic.twitter.com/vtOYRUQMJo — Matt Alba (@mattalbaWCBD) October 5, 2015

Dam breach leads to mandatory evacuation

A mandatory evacuation was ordered downstream from the Overcreek dam after a breach Monday, a spokeswoman for the city of Columbia said.

MANDATORY EVACUATION: OVERCREEK RESIDENTS LIVING BETWEEN FOREST DR. & PERCIVAL RD. IN FOREST ACRES — SCEMD (@SCEMD) October 5, 2015

Thom Berry, a spokesman with the South Carolina Emergency Management Division, said there was no major damage reported as a result of the breach. Overall, he said eight -- possibly nine -- dams have failed so far.

"We have several others that are in the process of being over-topped," he said.

Haley said more evacuations are likely as floodwaters rise in spots, and authorities warned of the danger of roads that look OK on the surface but that may have been undermined by raging waters.

Residents urged to stay off roads

The most acute danger is south of Columbia, where as much as 20 inches of rain fell between Friday and Sunday. In that area, authorities remain in emergency response mode amid widespread flooding. North of the city, authorities have shifted to assessment and recovery mode -- evaluating damage to roads, bridges and other infrastructure.

Some 1,300 National Guard troops have been activated to help respond to the historic storm, supplementing more than 250 state troopers and other state workers in addition to assessment crews from the federal government and other states, authorities said.

Crews performed hundreds of water rescues. A helicopter crew rescued dozens more, the governor said.

State officials urged people to stay off the roads. Haley said county officials would make decisions about closing their offices, and the state would follow suit in those locations. She said private businesses are not required to follow those decisions, but she encouraged them to do so.

She also urged people not to travel to flooded areas to gawk.

"This is not the time to take pictures," she said.

About 550 roads and highways remained closed in the state, acting Transportation Secretary Christy Hall said, including 100 bridges and roads in the Columbia area. More closures are expected as waters flow toward the coast, she said.

State emergency officials said Columbia residents should boil their drinking water.

JUST WATCHED Flash flood emergencies spread in South Carolina Replay More Videos ... MUST WATCH Flash flood emergencies spread in South Carolina 01:54

"Rising water from flooding can carry viruses, bacteria, chemicals and other submerged objects picked up as it moves through stormwater systems, across industrial sites, yards, roads and parking lots," the South Carolina Emergency Response Team said.

One bit of good news: No hospitals in the state will have to evacuate, as had been earlier feared, Haley said.

The governor said she had phoned in a request for a major disaster declaration to the federal government, seeking immediate aid in 11 counties -- a list expected to grow. President Barack Obama signed a disaster declaration Saturday, retroactive to Thursday.

Haley also said she had talked to Obama, who offered his condolences and prayers as the state begins what the governor said would be a long assessment and recovery.

Photos: Storms flood East Coast Photos: Storms flood East Coast This aerial photo shows flooding around Aberdeen Country Club in Longs, South Carolina, on Tuesday, October 6. South Carolina experienced record rainfall amounts over the weekend, forcing hundreds of evacuations and rescues. Hide Caption 1 of 37 Photos: Storms flood East Coast A woman uses her boat to check on neighbors and see if they want to evacuate in Summerville, South Carolina, on Monday, October 5. Hide Caption 2 of 37 Photos: Storms flood East Coast Police officers carry a woman to dry land after she was rescued from her home in the St. Andrews area of Columbia, South Carolina, on October 5. Hide Caption 3 of 37 Photos: Storms flood East Coast Neighbors and friends help clean up a home affected by flooding in Columbia on October 5. Hide Caption 4 of 37 Photos: Storms flood East Coast Five-month-old Jeremiah Odum, left, and his 2-year-old brother, Braxton Odum, nap on a cot in a high school gymnasium being used as a Red Cross shelter for flood evacuees in Rowesville, South Carolina, on October 5. Hide Caption 5 of 37 Photos: Storms flood East Coast Rescue teams wait for an emergency vehicle in the Forest Acres neighborhood of Columbia on Monday, October 5. Hide Caption 6 of 37 Photos: Storms flood East Coast An oil sheen floats atop floodwater in a subdivision west of the Ashley River in Charleston, South Carolina, on October 5. Hide Caption 7 of 37 Photos: Storms flood East Coast A dog is cut off from its home in Florence, South Carolina, on October 5. Florence is about 85 miles east of the capital city, Columbia. Hide Caption 8 of 37 Photos: Storms flood East Coast Hunter Baker drives his boat down a flooded East Black Creek Road to his home following heavy rains in Florence on October 5. Hide Caption 9 of 37 Photos: Storms flood East Coast A man makes his way through floodwaters in the parking lot of The Citadel Beach Club on Isle of Palms, South Carolina, on October 5. Charleston and surrounding areas are still struggling with flooding, as are areas 100 miles inland. Hide Caption 10 of 37 Photos: Storms flood East Coast Members of Norfolk Fire-Rescue pull a man from his car in Norfolk, Virginia, on Sunday, October 4. Hide Caption 11 of 37 Photos: Storms flood East Coast David Linnen takes a yard rake to clear drains in front of the Winyah Apartments in Georgetown, South Carolina, on October 4. Hide Caption 12 of 37 Photos: Storms flood East Coast Charlene Stennis is escorted to safety after her son was rescued from a stranded vehicle during the heavy rains on October 4 in Columbia, South Carolina. Hide Caption 13 of 37 Photos: Storms flood East Coast The roof of a submerged vehicle peeks above the flood waters on October 4 in Columbia, South Carolina. Hide Caption 14 of 37 Photos: Storms flood East Coast Tripp Adams, 8, walks through flood waters in Georgetown, South Carolina, on October 4. Hide Caption 15 of 37 Photos: Storms flood East Coast A person walks through the flooded Market and Water streets in downtown Wilmington, North Carolina, on October 4. Hide Caption 16 of 37 Photos: Storms flood East Coast Neighbors watch employees with the city of Isle of Palms, South Carolina, cut a live oak tree that fell after heavy rain on October 4. Hide Caption 17 of 37 Photos: Storms flood East Coast A man watches as a vehicle tries to navigate flood waters in Florence, South Carolina, on October 4. Hide Caption 18 of 37 Photos: Storms flood East Coast Two men row a boat on a flooded street in downtown Charleston, South Carolina, on October 4. Hide Caption 19 of 37 Photos: Storms flood East Coast Police block an entrance to Highway 17 in Charleston, South Carolina, on October 4. Hide Caption 20 of 37 Photos: Storms flood East Coast A man paddles up to a flooded store in Columbia, South Carolina, on October 4. Hide Caption 21 of 37 Photos: Storms flood East Coast A firefighter walks down a flooded street in downtown Charleston, South Carolina, on October 4. Hide Caption 22 of 37 Photos: Storms flood East Coast A worker cleans a drain on a flooded street in downtown Charleston, South Carolina, on Saturday, October 3. Hide Caption 23 of 37 Photos: Storms flood East Coast A utility worker examines the damage to a home Charlotte, North Carolina, on October 3. Hide Caption 24 of 37 Photos: Storms flood East Coast A motorist turns back as floodwater rises in Harrisburg, North Carolina, on October 3. Hide Caption 25 of 37 Photos: Storms flood East Coast A woman walks through One City Plaza in downtown Greenville, South Carolina, as rain and wind pound the area on October 3. Hide Caption 26 of 37 Photos: Storms flood East Coast Bob Ashbaugh, from Pittsburgh, takes video of waves crashing over homes at risk from erosion during high tide in Isle of Palms, South Carolina, on October 3. Hide Caption 27 of 37 Photos: Storms flood East Coast Stuart Tait ties together wood after his house collapsed into an inlet on Grassy Sound during high tide on October 3 north of North Wildwood, New Jersey. Hide Caption 28 of 37 Photos: Storms flood East Coast Will Cunningham, 14, rides his bike down Station 29 on Sullivan's Island, South Carolina, ahead of his paddling friend Patrick Kelly, 14, on October 3. Hide Caption 29 of 37 Photos: Storms flood East Coast Paul Banker paddles a kayak as his wife, Wink Banker, takes photos on a flooded street in Charleston, South Carolina, on October 3. Hide Caption 30 of 37 Photos: Storms flood East Coast Up to 4 inches of rain could strike the waterfront between Georgia and New Jersey. Motorists deal with the conditions on Friday, October 2, in Seaside Heights, New Jersey. Hide Caption 31 of 37 Photos: Storms flood East Coast Workers install a flood barrier at the entrance to the Market Pavilion Hotel in downtown Charleston, South Carolina, on Friday, October 2. Parts of the South Carolina coast braced for likely flooding. Hide Caption 32 of 37 Photos: Storms flood East Coast Flooding engulfs a neighborhood in the Strathmere section of Upper Township, New Jersey, on October 2. Hide Caption 33 of 37 Photos: Storms flood East Coast Sandbags surround a building in Old Town Alexandria, Virginia. Hide Caption 34 of 37 Photos: Storms flood East Coast A man closes a storefront on October 2 in Seaside Heights, New Jersey. Hide Caption 35 of 37 Photos: Storms flood East Coast Floodwater rises along Central Avenue in Sea Isle City, New Jersey, on October 2. Hide Caption 36 of 37 Photos: Storms flood East Coast Cars negotiate flooded streets on October 2 in Midland Beach on Staten Island, New York. Hide Caption 37 of 37

Storm brings massive flooding

The situation is the result of a weather system that funneled tropical moisture into South Carolina and refused to move on, CNN meteorologist Chad Myers said.

"It was a garden hose that just kept pouring ashore in one spot, and that spot was South Carolina," he said.

State officials described it as a 1,000-year storm -- referring to weather terminology describing a storm with a 1-in-1,000 chance of happening in any given year.

"This is an incident we've never dealt with before," Haley said Sunday.

While the rain is beginning to move out of the region, as much as an additional 2 inches could fall, Myers said. But some rivers may not crest for possibly two weeks, he said, meaning parts of the state will be dealing with flooding for some time.