The level in the massive man-made lake reached its peak of 902.59 feet at about 3 a.m. Sunday and dropped to 898 feet by 4 a.m. Monday, according to the Sacramento Bee. Water flows over the emergency spillway at 901 feet.

“The drop in the lake level was early evidence that the Department of Water Resources’ desperate attempt to prevent a catastrophic failure of the dam’s emergency spillway appeared to be paying dividends,” the Bee reported Monday.

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Officials doubled the flow of water out of the nearly mile-long primary spillway to 100,000 cubic feet per second, with the hope of lowering the lake level by 50 feet to leave room for upcoming rain. The normal flow is about half as much, but increased flows are common at this time of year, during peak rain season, officials said.

Officials also warned that damaged infrastructure could create further dangers as storms approach in the week ahead. During a midday news conference on Monday, they said they’re continuing to monitor the spillways for erosion. It also remains unclear when residents will be allowed back into their homes. Inmates at the Butte County Jail also have been moved to Alameda County about 170 miles away.

“I recognize that this is displacing a lot of people,” Butte County Sheriff Kory Honea told reporters. “We did this because our primary purpose is to ensure public safety. It was a hard decision to make.”

An early-morning inspection of the main spillway revealed no additional erosion, the Bee reported, and the Department of Water Resources said water would continue to flow at 100,000 cubic feet per second.

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Officials also will have to determine whether the damaged primary spillway will be able to handle high levels of water through the rest of the rainy season, Jay Lund, a civil engineering professor at the University of California at Davis, told the Bee.

Lake Oroville is one of California’s largest man-made lakes, with 3.5 million acre-feet of water and 167 miles of shoreline. And the 770-foot-tall Oroville Dam is the nation’s tallest, about 44 feet higher than the Hoover Dam on the Colorado River. The lake is the linchpin of California’s government-run water delivery system, sending water from the Sierra Nevada for agriculture in the Central Valley and for residents and businesses in Southern California.

After a record-setting drought, California has been battered by potentially record-setting rain, with the Northern California region getting 228 percent more than its normal rainfall for this time of year. The average annual rainfall of about 50 inches had already been overtaken with 68 inches in 2017 alone.

There was never any danger of the dam collapsing. The problem was with the spillways, which are safety valves designed to release water in a controlled fashion, preventing water from topping over the wall of the colossal dam that retains Lake Oroville.

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Earlier this month, unexpected erosion crumbled through the main spillway, sending chunks of concrete flying and creating a large hole. Then sheets of water began spilling over the dam’s emergency spillway for the first time in its nearly 50-year history.

Water from rain and snow rapidly flowed into the lake, causing it to rise to perilous levels, and sending water down the wooded hillside’s emergency spillway, carrying murky debris into the Feather River below.

“Once we have damage to a structure like that, it’s catastrophic,” Bill Croyle, acting director of the state’s Department of Water Resources, said at a news conference late Sunday, in reference to the erosion of the main spillway. “We determined we could not fix the hole. You don’t just throw a little bit of rock in it.”

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Anticipating a possible catastrophe for the Lake Oroville area, located about 75 miles north of Sacramento and about 25 miles southeast of Chico, the Butte County Sheriff’s Office ordered evacuations, adding in a news release that it was “NOT a drill.”

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But as the reservoir’s water levels lowered, the flows over the emergency spillway ceased late Sunday night.

California Gov. Jerry Brown (D) issued an emergency order to boost the state’s response to the evacuation efforts and spillway crisis, which Brown called “complex and rapidly changing.” The Federal Emergency Management Agency sent an incident management team to the governor’s Office of Emergency Services.

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Despite the minimized threats, Honea, the sheriff, said that he would not be lifting the mandatory evacuation order until water resources officials had a better grasp on the anticipated risks.

See photos as thousands are evacuated after Oroville Dam threatens floods share Share View Photos View Photos Next Image OROVILLE, CA - FEBRUARY 17: In this Handout provided by the California Department of Water Resources (pixel.water.ca.gov), Water continues to move down the damaged spillway at Oroville Dam with an outflow of 80,000 cubic feet per second (cfs) on on February 17, 2017 in Oroville, California. Last weekend overflow waters from the emergency spillway eroded much of the area below the spillway. The California Department of Water Resources continues to examine and repair the erosion with more than 125 construction crews working around the clock, and placing 1,200 tons of material on the spillway per hour using helicopters and heavy construction equipment at the Butte County site. (Brian Baer/ California Department of Water Resources via Getty Images)

The evacuation took residents by surprise.

April Torlone, 18, was at work at a Dollar General in Live Oak, Calif., Sunday evening when she received a flood emergency alert on her phone. She hurried home, she said, where she had about 10 minutes to gather some clothes and her late father’s ashes.

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Torlone drove with her mother and sister to her grandmother’s house in Sacramento, arriving well after midnight. The roughly 40-mile trip took six hours, she said. Gas stations were packed and stores were running out of food. Along the way, they saw more than 30 people camped out in their cars on the side of the road, many with trunks full of belongings, Torlone said.

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“I just hope everyone is safe and finds a place to stay, and that no one’s homes are damaged,” she told The Washington Post. “It’s honestly so sad.”

Shelters, churches, schools and seven Sikh temples opened their doors, and people offered to open their homes to strangers via Twitter messages. Hotels and motels out of harm’s way filled up quickly, creating communities of the suddenly displaced. Beale Air Force Base, east of Marysville, also opened its gates to area residents and said early Monday that it had received approximately 250 evacuees.

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The dam itself remained structurally sound, the state Department of Water Resources said, and officials said helicopters would be deployed to drop bags of rocks into the crevice and prevent any further erosion.

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Croyle, the acting Department of Water Resources director, said Lake Oroville would need to lower almost 50 feet to reach levels at which the system would normally operate. Croyle said that personnel were unable to access the eroded emergency spillway Sunday to do repair work. Officials aimed to continue to discharge as much water as possible ahead of upcoming storms, without adding too much pressure to the already damaged infrastructure.

“Our goal is to be able to use that infrastructure throughout this wet season,” Croyle said. Forecasts indicate that dry weather will dominate through Tuesday, but a series of Pacific storms are expected to arrive across the region Wednesday into Thursday, bringing up to four inches of rain to parts of the Central Valley, according to the National Weather Service.

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Honea called the evacuation order a “critical and difficult decision” and said he recognized it would cause significant dislocations and traffic jams, which it did. Residents of Oroville, a town of 16,000 people, were ordered to head north toward Chico, while other nearby residents drove south toward Sacramento.

“I recognize how tough this situation is on people,” Honea said Sunday night. “I recognize that we’ve had to displace a lot of people.”

The California National Guard will provide eight helicopters to assist with emergency spillway repair, Adjutant General David S. Baldwin said. All 23,000 soldiers and airmen statewide received an alert to be “ready to go if needed,” Baldwin said. The last time such an alert was sent out to the entire California National Guard was the 1992 Los Angeles riots, which erupted after a trial jury acquitted four officers of the Los Angeles Police Department of the use of excessive force in the videotaped arrest and beating of Rodney King.

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Officials said 250 law enforcement personnel were being deployed to patrol the evacuated areas.

Travelers reported traffic at a standstill on some routes, especially on Highway 99 between Oroville and Chico.

Nicholas Mertz, a front desk supervisor at Oxford Suites Chico, told The Post that when he started his shift at 3 p.m. on Sunday, the hotel’s 184 rooms were at 54 percent occupancy, but within an hour or two, the rooms reached full capacity. What began as a normal night quickly turned into “hectic craziness, everything all at once,” Mertz said. The hotel’s five phone lines were ringing nonstop, and hundreds of guests came pouring in.

“It’s never happened that fast,” Mertz said. Larger families of five to eight people packed into rooms, without having to pay the usual fees for additional guests, Mertz said, because “in this scenario, it’s whatever you can do.”

Many guests expressed confusion and frustration, while others spoke of their fears: What would happen to the pets they left behind? Would there be looting in the evacuated neighborhoods? Would their homes still be standing when they returned?

“Not only are you just a front desk person you’re kind of like a therapist as well,” Mertz said.

Kyle Dobson, 41, said he was visiting the dam Sunday afternoon from Yuba City, Calif., and noticed that the lake was higher than he had ever seen it. He said he got a call later in the day that Oroville was being evacuated. By the time he got home, Yuba City had also been ordered to evacuate.

Dobson said he and his wife packed about a week’s worth of clothes for themselves and their four young children, and moved pictures and other belongings to the second floor of their two-story home. For now, they are staying put, but if the situation gets worse, they will drive to Sutter, Calif., to stay with family, Dobson said.

“I’ll stay up probably all night, listen to the police scanner and watch the reports come in,” he said. “The river levels — that’s what you’ve got to watch out for.”

Adriana Weidman of Marysville, Calif., said she heard about the evacuation around 5 p.m. Fearing that nearby rivers would overflow, she rushed to pack as much as she could, then got into the car with her husband and two children, she said. By 10 p.m., the family was still sitting in gridlocked traffic on the way to Colfax, Calif., about 45 miles east.

“It’s scary,” Weidman told The Post. “I’m terrified I’m not going to have a home to come home to.”

Out of an “abundance of caution,” inmates were in the process of being evacuated from the Butte County Jail Sunday night, the sheriff’s office wrote on Facebook.

“We needed to get people moving quickly in order to protect the public and save lives if the worst case scenario did come to fruition,” Honea said.

The damaged primary spillway caused water flowing downstream to become muddy and brown with debris earlier this week, threatening the lives of millions of baby Chinook salmon in the Feather River Hatchery below. In a rescue operation, officials with the California Department of Fish and Wildlife successfully moved about 5 million Chinook salmon to a nearby annex, the department said on Facebook.

The other 3 million baby salmon will remain at the main hatchery, where staff and engineers have rigged a system of pumps, pipes and generators and a sediment pond in the hopes of filtering the water enough to support the fish.

Ironically, the state’s five years of drought caused Lake Oroville’s water levels to plunge to a low of 33 percent of capacity, according to the Los Angeles Times. The lake became a poster child for the drought. In a dramatic shift, Northern California witnessed an extraordinarily rainy winter this year that caused waters to rise to their highest levels in decades.

This post has been updated.