A large portion of a house teetering on the edge of the Blue Earth River near the Rapidan Dam fell into the water late Tuesday, according to authorities.

"A portion of the house on the property closest to the Rapidan Dam has been undercut enough to have fallen into the river," the Blue Earth County Sheriff's Office said in a statement. "Blue Earth County Public Works, Emergency Management and Sheriff's Office are monitoring for downstream impacts."

The house belongs to an area family that has operated the Rapidan Dam Store for decades. The store has a café well known by residents in the area for its pies and hamburgers.

Jenny Barnes, who makes the pies, and her brother, David Hruska, who makes the hamburgers, visited their childhood home Tuesday afternoon in the hours before the house collapsed.

Barnes, whose father, Jim Hruska, bought the cafe in 1972, said on Tuesday that she had been mentally preparing herself to lose her childhood home.

"We know we're losing the house," Barnes said next to the house on Tuesday afternoon. "We know that for sure. There's no going back inside the house."

Barnes said she had been in the dam store after midnight on Monday morning, making pies for the next day.

That's when she heard a loud boom. She ran out and saw that water was rushing over the top of the Rapidan Dam, just a few dozen yards away. She recalled hearing more explosions and saw sparks flying as water tore into an electrical substation near the dam and eventually pulled it into the river.

David Hruska said he and his father were in the house that night when the dam started overflowing. He said someone woke him up and told him to go outside. There he saw a shed owned by the county fall into the river.

They did not know it at the time, but floodwaters fed by recent rains had swept dead trees into the dam, jamming its five steel gates. The Rapidan Dam hasn't produced electricity in a number of years after floods in 2019 and 2020 rendered it inoperable.

Early Monday night, rushing water, part of the second-strongest flood ever recorded at the dam, carved a channel around the dam's west edge, washing away the soft earth.

The family called 911 and had just a half hour or so to evacuate the house and save family photos and other possessions gathered over decades. The family is now staying at Barnes' home, 2 miles away.

The dam has held since getting swamped earlier this week, with water flowing over and around the structure and relieving some of the pressure, county officials said.

"We believe it's intact and it will hold," Blue Earth County Emergency Management Director Eric Weller told the Star Tribune early Tuesday.

June rains in the Mankato area flooded basements and closed numerous roadways along the Minnesota River, which crested Wednesday at 29.7 feet, according to a statement from the city of Mankato.

Weller said Wednesday the county was hearing from engineers the river was too high for major work to shore up the west abutment. "We need the water to go down so we can do emergency stabilization," he said.

On Tuesday, the Federal Energy Regulatory Commission sent a letter to Blue Earth County asking to discuss risk reduction steps needed to prevent a complete breach of the dam from the eroded river. The letter, distributed to media early Wednesday and signed by regional engineer Kevin Griebenow, said the county "must consider methods to reduce the debris blockage at the gated spillway section."

"Further stabilization measures will be necessary once the immediate threat to the project has passed," wrote Griebenow, who in June had informed the county that the Rapidan Dam passed a FERC inspection.

Minnesota officials are reminding residents to stay safe amid the flooding.

"As we watch the house that was on that cliffside and the erosion of the hillside there I think it just goes to show how incredibly powerful that water is. It's just a reminder on how important it is to stay away from any moving water and things can rapidly change in a very, very split second," T. John Cunningham, an assistant commissioner with the Minnesota Department of Public Safety, said at a news conference on Wednesday.

David Hruska said his father, Jim Hruska, has not been taking the loss of the house well. He said his father wanted to stay at the house Monday night, even after everything that had happened. On Tuesday, he said his father did not want to see the house at all.

David Hruska said his father has dementia, adding that his dad must also be dealing with denial that a home filled with five decades of memories would be lost.

"He knows, but I don't know if he wants to believe it," David Hruska said.

He paused. "I've been that way too," he said. "Hard to believe what's going on."

But both siblings said they plan to continue with the store as long as Mother Nature and the county comply.

"We're going to reopen, we're going to keep selling those burgers and pie and milkshakes," Barnes said.

"We have no plans of not opening the dam store," David Hruska said. "The dam store's going to stay going, as long as we have the say to do it."

Star Tribune staff writer Walker Orenstein contributed to this story.