Southern Minnesota motorists know the stretch of road well.

Right where the Jolly Green Giant billboard stands grinning on a hillside, U.S. Hwy. 169 dips from the prairie down into the wooded lowlands below Le Sueur.

Unlike vast stretches of the farm-rich region, the highway here bellies up to the undulating blue ribbon of the Minnesota River, which, during wet months, can rise nearly to motorists' eye level.

It's both natural marvel and foe. Tornadoes whip through the valley. Ice can cake narrow roadways. And then there's the rain, which can swell this seemingly tamed waterway into a monster roaming up into the hills.

Over the years, the Minnesota River (and nearby roadways) have flooded often. The years are like notches on a doorway: 1965, 1993, 2019.

As often, stretches of Hwy. 169 north from Mankato and St. Peter downstream through Le Sueur and near Henderson have been closed.

Earlier this century, state officials poured millions into Hwy. 169, including renovating a steel bridge that spans south-central Minnesota's mightiest waterway outside Le Sueur.

The hope was that the roadway could withstand even a once-in-a-century flood. Emergency vehicles, grain trucks and visitors from the Twin Cities might then avoid detours or cancelled trips.

Then came the 2024 floods.

As of Thursday morning, the highway between Le Sueur and St. Peter remains closed for the third day in a row. Meanwhile, that highway between Mankato and St. Peter is back open.

In an Air National Guard hangar in St. Paul on Tuesday — after an aerial tour that brought Gov. Tim Walz and Sen. Amy Klobuchar hovering over the imperiled Rapidan Dam southwest of Mankato, and the dramatic flooding in Waterville — Walz noted that, after providing safety for residents, those charged with rebuilding structures need to deal with a new normal of extreme weather.

"If I recall right, the engineers built [that bridge over the Minnesota River] for a 500-year flood," Walz said. "That was 14 years ago. So, the 500-year flood came in 14 years."

State officials confirmed on Wednesday that the bridge that opened in 2008 was actually built to withstand a 100-year-flood.

It's far from the only flooded road. By midweek, the bridge on Hwy. 93 into Le Sueur was underwater.

"That bridge deck has never been fully underwater in its history," said Joe Roby, Le Sueur's city administrator. "That is one of the only east-west crossing points over the river between Mankato and Chaska."

Flooding is a geography lesson in a region's interconnected river and transportation system — and a sleepless exercise for workers. By Wednesday, Minnesota Department of Transportation crews had opened one northbound lane on Hwy. 169, as crews pumped water off the highway.

Roby watched in amazement from his hometown. Just a few months ago, he said, with the state deep in drought, his 6-year-old daughter could throw a stone across the Minnesota River.

At a news conference on Wednesday, Lt. Gov. Peggy Flanagan stressed that detours are a public safety necessity.

"I also know that having 169 being closed can be an annoyance," Flanagan said. "But it's really, really important for people to follow those detours, to stay safe and to avoid driving through any water."

"169 is a huge corridor of commerce," Roby said. "There's a tremendous amount of people and goods and services who rely on getting to and from the metro, from Iowa or the Mankato area, or Worthington or South Dakota. It's really extraordinary."

And a changing climate necessitates better preparation for extreme weather.

During Tuesday's news conference, Klobuchar spoke about flood mitigation efforts in Duluth and Austin after flooding damaged homes and businesses.

"We do know we save communities in future flood[s] when we do something now preventative," she said.

Klobuchar noted that her own husband and daughter were stymied in their attempts to visit family in Mankato.

Like other Minnesotans, they will need to wait for the river to slowly return to its banks.

"When you see all the water," Klobuchar said, "you understand what's going on."