The governor said that officials in Butte County were forced to use emergency spillway at Lake Oroville Dam.
“I’ve been in close contact with emergency personnel managing the situation in Oroville throughout the weekend and it’s clear the circumstances are complex and rapidly changing,” Brown said in a statement.
The governor said that officials in Butte County were forced to use emergency spillway at Lake Oroville Dam after massive amounts of rainfall in January and February led to maximum capacity water levels at the lake.
But officials soon realized the spillway, about 125 km north of Sacramento, was in danger of failing after suffering severe erosion, leading to the evacuation of tens of thousands from their homes.
The state of emergency was declared in Butte, Sutter and Yuba counties.
“The state is directing all necessary personnel and resources to deal with this very serious situation,” Brown said.
Some 188,000 residents had been ordered to evacuate.
Butte County Sheriff Kory Honea said no decision had been made on when people will be allowed back into their homes, the Sacramento Bee reported.
Some 100 California Highway Patrol officers had been sent to the region and 1,200 California National Guard members had been sent notice that they may be needed, according to the report.
Evacuees hurrying away from low-lying areas jammed local highways and gas stations and made last-minute hotel bookings, the Sacramento Bee reported. The wide-ranging evacuation orders covered an area with more than 160,000 residents, the paper said.
In issuing its initial evacuation orders, the state’s Water Resources Department tweeted about 4:45 pm (0045 GMT) that the emergency spillway could fail “within the next hour.”
In the ensuing hours, the department sent more water down the dam’s main spillway, in an effort to “avert more erosion at the top of the auxiliary spillway,” the department said in a statement.
A massive hole that opened up last week in the dam’s main spillway led to the use of the emergency spillway, the first time it had been used in the dam’s 48-year history, the water department said.
The Oroville Dam itself – the nation’s tallest, at nearly 235 metres, “is sound and is a separate structure,” the water department said.
California, which has faced a drought in recent years, has seen heavy rain and snowfalls this winter.