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Post-storm mop-up in Cook, Minn., started off easy enough Wednesday morning. But by afternoon, water — waist-deep in some parts — filled several downtown blocks.

The river rose and "you couldn't stop it," resident Kim Brunner said of the Little Fork River that runs through the city of 522 about 90 miles north of Duluth.

Businesses are shut down, roads are blocked off and "everything is at a standstill," Brunner said, as water continued to rise.

The damage in Cook and vast swaths of Northeast Minnesota prompted St. Louis County to declare a disaster Thursday after the Tuesday night storm that drenched the region, flooding residential areas and cleaving some roads in half. About 170 campers at the YMCA Camp du Nord near Ely were stuck behind a washed-out road.

The County Board held an emergency meeting to ensure the county was eligible for federal and state relief aid. Commissioner Keith Nelson estimated at least $50 million in damages thus far, and county leaders said the storm ranks as the second-largest natural disaster in three decades, after a 2012 flood. Gov. Tim Walz is expected to survey damage in Biwabik, Minn., and Cook on Friday, with DFL Senate Majority Leader Erin Murphy and Sen. Grant Hauschild, DFL-Hermantown.

It's critical to secure state support for rural areas that don't have the resources of larger cities, Hauschild said.

"The community [of Cook] is really coming together ... and the state needs to step up as well," he said.

The northeastern Minnesota city of Cook is under water Thursday after nearby Little Fork River crested following 5 inches of rain. | City of Cook Public Works
The northeastern Minnesota city of Cook is under water Thursday after nearby Little Fork River crested following 5 inches of rain. | City of Cook Public Works

Between 5 and 7 inches of rain fell around Cook. But floodwaters are not just from rain there, said Joe Moore, with Duluth's National Weather Service.

The river's headwaters absorbed and then released rain, adding to the swollen Little Fork.

More than 40 roads were closed inside the state's largest county, with the most damage confined to the upper third. Standing water, blown-out culverts and erosion triggered most of the closures. County officials asked drivers to turn around at barricades — many vehicles stalled in high water after ignoring them.

With more rain expected in the coming days, "the entire county is at risk," said Jim Foldesi, its public works director. "This could easily go from what we see now to a 2012 level event. Any more water that we get ... is going to immediately run off."

Pre-evacuation notices are being delivered to Cook residents in anticipation of rising waters, with the city "in dire straits right now," St. Louis County Commissioner Michael Jugovich said. "There are canoes going down the street."

On Thursday, the county prioritized dead-end roads with washouts that left people trapped, including the one leading to Camp du Nord. Officials could not yet estimate how many people are affected but said many of the properties in that situation are seasonal.

As some roads reopen, others downstream are expected to close as water moves through the region. Minnesota Power has been releasing water from a reservoir near Duluth to make room for water arriving from farther north. Discharge from Whiteface Reservoir, about an hour north of Duluth, was "increased substantially" Thursday because the reservoir was nearly full, said Nora Rosemore, manager of renewable business operations for Minnesota Power.

"We are using the little bit of storage we have in these reservoirs and the timing of our discharges to lessen the flood impacts downstream while maintaining the integrity of the dams," she said.

Rising water reportedly washed out some railroad tracks in northern St. Louis County, on a critical artery traveling from Canada. Canadian National Railway didn't immediately return a message.

A major washout exposed the Biwabik, Minn., underground utilities infrastructure, affecting the water supply to the areas near Giants Ridge and the Voyageurs Retreat development. A decrease in water pressure created the potential for contamination, according to a news release from the Gilbert Police Department. Biwabik was able to connect its water system to that of the nearby town of Aurora.

Water had been restored by Wednesday night, but residents were still being asked to boil drinking water into Thursday afternoon.

Lake and Cook counties experienced flash flooding and downed trees. Severe flooding at Gooseberry Falls State Park has closed several of its trails and day-use areas.

Nelson said cleanup shouldn't prevent visitors from heading to northeastern Minnesota. Thousands are scheduled to descend on the area for Grandma's Marathon weekend.

"We want people to continue to come north," he said.

Staff writer Christa Lawler contributed to this story.