MOUNT VERNON, Wash. — Surging floodwaters turned farmland into vast pools, washed out bridges and prompted rescues of people stranded in cars and homes across Washington state on Thursday, as tens of thousands of people were under evacuation orders and authorities hoped levees would hold and prevent far worse damage.

“The flooding levels we’re looking at are potentially historic in nature, so we just want to emphasize how serious the situation is,” Gov. Bob Ferguson said at a news briefing Thursday, one day after declaring a statewide emergency. “This situation is extremely unpredictable.”

Skagit County, in a major agricultural region north of Seattle, has ordered everyone within the Skagit River’s floodplain to evacuate. Some 78,000 people live in the floodplain, according to the county’s emergency management chief Julie de Losada.

The high water mark upstream at the town of Concrete was below estimates but authorities warned people that record levels elsewhere were still possible.

Along the river in Mount Vernon, teams knocked on doors in low-lying areas Thursday to inform them of evacuation notices, city authorities said. Further north near the U.S.-Canada border, firefighters rescued several people from their homes in Sumas, the mayor said.

Over 10,000 customers in Washington were without electricity late Thursday afternoon, according to PowerOutage.us. A mountainous section of U.S. 2 was closed due to rocks, trees and mud, with no detour or estimated time for reopening, according to the state transportation department.

Heavy rain and flooding washed out at least three bridges in the mountains of northwestern Montana, where an emergency shelter opened in a church in the small town of Libby.

The Skagit River hit about a foot (30 centimeters) shy of the previous record in the mountain town of Concrete Thursday morning, according to the National Water Prediction Service.

While updated projections are lower than previous estimates, the river was still expected to crest above the record in Mount Vernon on Friday.

Flooding from the river has long plagued Mount Vernon, the largest city in the county with some 35,000 residents. Flooding in 2003 displaced hundreds of people.

A floodwall that protects downtown passed a major test in 2021, when the river crested near record levels. Water was at the foot of the floodwall as of late Thursday morning, Donovan said.

In nearby Burlington, officials hoped dikes and other systems would protect the community from catastrophic flooding, said Michael Lumpkin, with the police department.

Some are worried that older levees could fail. Business owners and residents stacked sandbags to protect buildings.