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South Carolina officials warned Monday that the dangers from the state's unprecedented floods weren't over — and that clearing skies didn't erase the threat of shifting water and unstable roads.

At least 12 weather-related deaths in the Carolinas were blamed on the vast rainstorm — 10 in South Carolina and two in North Carolina.

South Carolina Gov. Nikki Haley said authorities were expecting to evacuate more people as the floodwaters flowed from the state's midlands to the coast.

"This is not over — just because the rain stops doesn't mean we are out of the woods," she told reporters. "Even though you're not seeing rain, there is still water out there."

The state Office of Emergency Management said at least eight dams across the state had been breached by flood waters. Residents near Forest Acres were being urged to evacuate after the Overcreek Dam was breached shortly after 3:30 p.m. ET, Columbia City Manager Teresa Wilson said.

Authorities, meanwhile, were concerned that water from Forest Acres could run into the Katherine Dam — causing it to breach and re-inundate areas of Columbia where floodwaters had receded.

President Barack Obama signed a disaster declaration Monday night, ordering federal aid to help recovery efforts. The declaration makes federal funding available to people in Charleston, Dorchester, Georgetown, Horry, Lexington, Orangeburg, Richland and Williamsburg counties.

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The Federal Emergency Management Agency said that damage surveys are continuing in other areas and that more counties could be designated for assistance.

By Monday evening, 365 state-maintained roads and 166 bridges were closed, the state Transportation Department said. Forty thousand people across the state remained without fresh running water, and 26,000 were without electricity.

Haley said 1,300 National Guard members were on duty and had performed 25 aerial rescues so far. Rescue teams were walking door to door to check on people stranded by the flooding.

"This is a Hugo-level event," said Maj. Gen. Robert Livingston, head of the state National Guard, referring to the September 1989 hurricane that devastated Charleston. "This water doesn't fool around."

Haley said that although the emergency services were shifting from a response to assessment mode, the state remains in a "vulnerable" situation after going through a storm it "has never seen before."

While Hurricane Joaquin missed the East Coast, it fueled a "fire hose" of tropical moisture aimed directly at the state, the weather service said. Parts of South Carolina were told to expect as much as three more inches of rain before the storm moved offshore.

The conditions prompted officials to warn residents not to leave their homes for any reason — even on foot. On top of the flood threat, the National Weather Service also warned of 30-mph winds gusts, increasing the risk of falling trees.

Columbia Fire Chief Aubry Jenkins said there had been too many rescues to keep count. Among those were 90 people in Irmo, 10 miles northwest of Columbia, who were forced to evacuate their homes by boat, NBC station WIS reported.

Meanwhile, authorities were establishing water distribution centers — four of which were expected to be up and running Monday, Haley said. Authorities in Columbia told all 375,000 of their water customers to boil water before drinking because of water line breaks and the threat of rising water to a treatment plant.

The record for the most rain in 24 hours had been 14.80 inches, set during Hurricane Floyd in 1999. That was smashed in several places, with some areas of the coast getting as much rain as they normally would in eight months, the National Weather Service said, reporting almost 25 inches in Kingstree, 24 inches in the town of Longs in Horry County and 21 inches in Georgetown.

Experts said parts of South Carolina experienced a "1,000-year flood event," meaning in any given year there is a 1-in-1,000 chance of that much rain.

"Ground zero" on Monday, was Myrtle Beach, where roads in the neighborhood of Cameron Village flowed like rivers.

"It's pretty flooded. It's a couple feet on every street," resident Jessie Poudrier told NBC station WMBF. "We were able to take kayaks out — that's the only way people are getting around."

Many rivers in major flood stage. Interactive map from Southeast River Forecast Center: http://t.co/V4jZMetmB3 #scwx pic.twitter.com/crY2pGdOBp — NWS WPC (@NWSWPC) October 5, 2015

For the most part, the storm has moved through and the region should be dry, said Kevin Roth, lead meteorologist for The Weather Channel.

"The end is in sight," Roth said. "This should be the last of any kind of rain for the next seven days."

But "rivers all through South Carolina are running exceptionally high and will cause further damage into Wednesday even though it will be sunny by then," he said.