Damage to the spillway was first noticed on February 7 and set off a series of actions by officials concerned that damage to an emergency spillway could dump large amounts of water into the Feather River, which runs through downtown Oroville.
The evacuation was ordered Sunday afternoon after engineers told authorities that a hole on the concrete lip of the secondary spillway for the dam could fail within the hour.
Honea said there was a plan to plug the hole by using helicopters to drop rocks into the crevasse.
"Immediate evacuation from the low levels of Oroville and areas downstream is ordered", the Butte County sheriff said in a statement posted on social media. Once Lake Oroville reached capacity, officials from California's Department of Water Resources began utilizing the dam's spillway - a structure that provides the controlled release of water.
As of 5 a.m., water was at 898.19 feet, a little more than a foot below the top.
Lake Oroville is one of California's largest man-made lakes, and the dam is 335-metres tall.
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A failure of the dam could send a 30-foot wall of water cascading into the surrounding towns along the Feather River Basin, causing potentially devastating flash flooding.
"The police came and told us to evacuate", said Kaysi Levias who was with her husband, Greg, at a gas station as they attempted to flee.
Water officials said they are relieving pressure on the spillway by increasing water flows down the primary concrete spillway, and that they have not seen any further damage today to the concrete, due to the additional water.
The Mercury News, a local newspaper, reported that three environmental groups - the Friends of the River, the Sierra Club and the South Yuba Citizens League - filed a motion with the federal government in 2005 as part of Oroville Dam's relicensing process, urging federal officials to bolster the dam's emergency spillway. "This is an evacuation order". But the damage costs appear to be mounting with the additional erosion damage to the emergency spillway.
The National Weather Service urged people living downstream of the tallest dam in the United States to flee to higher ground on Sunday, after authorities said that a damaged auxiliary spillway was on the verge of collapse. Rain is expected to begin falling later this week and continue through Saturday and Sunday.
Other areas now being evacuated include Marysville, Hallwood, Olivehurst, Gridley, Live Oak, Wheatland, Yuba City and Yuba County.