SOUTH BEND TOWNSHIP, Minn. (NewsNation) — A dam in Minnesota is in “imminent failure condition,” authorities have warned, posing a dangerous threat of putting thousands of residents in the path of uncontrolled floodwaters.

The Rapidan Dam on the Blue Earth River experienced a “partial failure” on its western support structure due to debris blockage, which caused water to erode the western bank, Blue Earth County said Monday afternoon on Facebook.

Officials provided an update on the dam’s condition Tuesday morning, saying it is now the second-largest flood on record at the Rapidan Dam. While there is still a high-level concern for flooding, Ryan Thilges, the Blue Earth County Public Works director, said their concern has begun to flatline.

“It’s more of an environmental concern if the dam were to totally breach because of the volume of sediment that is upheld upstream,” Thilges said.

No evacuations have been ordered yet as the state has faced serious flooding with the possibility of more rain in the forecast.

Residents downstream were under a flash flood warning through 10:30 a.m. ET Tuesday and are advised to monitor the situation closely and be prepared to evacuate if the dam fails.

Residents urged to leave the area

Eric Weller, emergency management director for the Blue Earth County sheriff, said the bank would likely erode more, but he didn’t expect the concrete dam itself to fail. Two homes downstream were evacuated.

Multiple areas of Blue Earth County have experienced flooding, prompting some residents in low-lying areas to evacuate.

Water was flowing at a rate of more than 30,000 cubic feet per minute, the equivalent of 20 Olympic-sized swimming pools.

Gov. Tim Walz said Monday on X, formerly known as Twitter, that emergency management is monitoring the situation.

What happens if the dam collapses?

There are tens of thousands of residents in the 21 cities in this river’s path. If there is a total breach, officials warn immediate evacuation orders will go into effect.

On Monday, the city of Mankato, Minnesota, reported the river level at 28 feet, with the dam built to hold 39.5 feet. Should the dam fail, there could be a surge of river water up to 2 feet.

Walz said the river is expected to reach 20 feet by the end of the week.

Xcel Energy has been barricading several facilities with sandbags and barriers to prevent floodwaters from causing a power disaster, CBS News reported. An Xcel Energy substation at the dam has already been washed away, affecting power for around 600 residents.

The dam was built in 1910 and has been weakened by repeated flooding over the decades. A 2019 Associated Press investigation into dams across the country found that the Rapidan Dam was in fair condition and there likely would be loss of property if it failed. A 2021 report recommended repair or removal, but Blue Earth County said on its website there was no danger to the public.

NewsNation’s digital producer Steph Whiteside and the Associated Press contributed to this report.