Thousands of people have been fleeing California towns below the overflowing Oroville Dam after fears of an imminent collapse of its emergency spillway prompted an evacuation order. Authorities are seeking to stem the breach with the help of helicopters.

“Immediate evacuation from the low levels of Oroville and areas downstream is ordered. This is NOT A Drill. This is NOT A Drill. This in NOT A Drill,” says the statement posted on the Butte County Sheriff’s Facebook page.

The statement refers to the Lake Oroville Dam, located 105 km (65 miles) north of Sacramento.
The dam’s spillway was “predicted to fail within the next hour,” the California Department of Water Resources (DWR) said at around 4:30pm PST Sunday (00:30 GMT Monday).

“DO NOT TRAVEL NORTH TOWARD OROVILLE,” the Yuba County Office of Emergency Services said on Facebook, urging evacuees to travel safely in all other directions and help the elderly.

DWR issued a statement, saying that there is no danger that the dam itself will collapse, as the incident had affected only an emergency spillway.

“Oroville Dam itself is sound and is a separate structure from the auxiliary spillway,” the statement read.

The emergency is the first time in the 48-year-old dam’s history that an uncontrolled spillway is being used, local NBC affiliate KCRA-TV reported.

Heavy rains and snow that struck California this winter have resulted in the dam’s reservoir being filled up to the point of overspill. On Thursday, the works to release water from the dam began after chunks of concrete from the spillway were discovered in the channel below.

On Friday, only 7 feet (2 meters) were left until the dam was to reach its full capacity.

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