Emergency evacuation of Yuba City and areas in Sutton County was ordered on Sunday following a warning that the damaged Oroville Dam could burst.
Water from the Cosumnes and Mokelumne rivers floods a house and barn after the erosion damaged the dam's main spillway What's happened to the emergency spillway?
Honea also said that the county meant to plug the hole in the dam by dropping sandbags and stones in it with a helicopter.
Officials said the spillway structure was predicted to fail early Sunday evening, creating a "hazardous situation", 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 wrote in a news release, adding that this was "NOT a drill".
The emergency spillway of the Oroville Dam in Northern California could fail within an hour unleashing uncontrolled flood waters from Lake Oroville, the California Department of Water Resources said on Sunday afternoon.
Heavy rains and snow that struck California this winter have resulted in the dam's reservoir being filled up to the point of overspill.
Butte County Sheriff Kory Honea has said the region was not yet safe, but officials were working on a plan for evacuees to return home. But with accumulating rain and snowmelt causing another overflow of the weakened emergency spillway by late Friday, there is a significant risk of heavy damage to the Oroville Dam spillways.
As crews worked to shore up the emergency section, water was re-routed back into the original damaged spillway in an effort to drain the dam as much as possible before the storms arrived. Officials earlier Sunday stressed the dam itself was structurally sound and said there was no threat to the public.More news: Raptors acquire Serge Ibaka from Magic for Ross, 1st-round pick
Those potential flows could exceed the capacity of downstream channels.
With the emergency evacuation orders in place due to the spillways, there are local schools that will be closed on Monday.
Water levels at Lake Oroville had gradually dropped from the beginning of the rainy season in October until December, when a series of strong storms hit the state.
Helicopters cary huge bags full of rock to stabilize the emergency spillway next to the Oroville Dam on Monday Feb. 13, 2017, in Oroville, Ca.
Some people had just a few minutes to prepare to evacuate, in what one Oroville resident described as "pure chaos".
California and local officials are rushing to fix the spillways at Lake Oroville and lower the water level by as much as 50 feet ahead of rain forecast for later this week.
Evacuation orders remain in effect for towns below the spillway, including Oroville, Gridley, Live Oak, Marysville, Yuba City, Olivehearst, Linda, and Wheatland.
At 770 feet (230 metres) high, the structure, built between 1962 and 1968, is the tallest dam in the United States, besting the famed Hoover Dam by more than 40 feet (12 metres).