State and local officials are trying to figure out how to repair damage caused by a flood of muddy water from an abandoned mine pit in northern Minnesota.

On April 24, water and sediment from the Hector Mine iron ore pit breached an earthen berm and flowed downstream into the Embarrass River and connecting lakes. It washed out utility lines and closed a stretch of the Mesabi Trail, popular in the summer for biking and walking.

Some mining opponents are pointing to the incident as a warning sign of the dangers of dam breaches and resulting spills.

The Hector Mine is a natural iron ore pit just north of the city of Biwabik, Minn. Mining ended there in 1953, and the open pit is full of water.

The trouble started last November when the water first breached the pit mine's earthen berm. Water and soil washed downstream and took out a part of the Mesabi Trail.

Then, on April 24, water that had been pooling in the mine overflowed its embankment, leaving a ravine up to 50 feet wide and 25 feet deep in places.

"It resulted in sort of the blowing out of all of the material between the pit and the river, creating a chasm," said John Thomas, an environmental specialist with the Minnesota Pollution Control Agency.

No one's sure about exactly what caused the failure. The Iron Range Resources and Rehabilitation Board, which owns the site, cited heavy fall rains, beaver dams and blocked drainage culverts as possible factors.

The April torrent washed into the Embarrass River, turning it a reddish brown. It continued downstream into the Embarrass, Cedar Island and Esquagama lakes.

"The water — all of the residents noticed as well — was quite muddy-looking, with an orange, kind of red iron-y tint to it," said Edie Evarts, area fisheries supervisor for the Minnesota Department of Natural Resources. "There was a lot of fine sediment in the water."

Evarts said that, so far, it doesn't appear the washout killed any fish. But she said some impacts might not be visible yet.

"A lot of the spawning fish that need clean, silt-free sediments, like walleye and northern pike — I wouldn't expect their success for spawning to be very good this year," Evarts said.

Debris and sediment from the washout clogged up the river channel and temporarily stopped the flow of water.

"There was zero flow coming from the Embarrass River to Embarrass Lake," said Kim Boland, an area hydrologist for the DNR. "It was completely blocked off."

That caused the upstream lake level to rise two feet until construction crews could remove the debris and get the river flowing again, Boland said.

The washout also broke water and sewer lines that serve the Giants Ridge recreation area, a golf and ski resort. The break released an estimated 10,000 gallons of sewage that also flowed downstream.

"When the ground cut loose, those lines were completely ripped out," said Jeff Jacobson, Biwabik city administrator.

The city restored water access to businesses and residents by creating an emergency bypass to the nearby city of Aurora, Minn., he said.

Jacobson said engineers are working on a plan to replace the damaged utility lines as well as a longer-term fix to prevent another washout at the mine.

No one's sure exactly what caused the berm failure. But despite the damage, things could have been worse.

It happened in springtime, so the lakes were still covered with ice. Any pathogens from the spill couldn't survive long in cold conditions, Thomas said. And he said any contaminants would have been diluted with billions of gallons of water in the lakes.

"The risk of exposure to that water is probably no greater than the typical risk that anyone runs by swimming in any lake of Minnesota," Thomas said.

It's too early to know how much it will cost to fix the damage — or who will pay for it.

The mine was closed, so there's no company to hold financially responsible. The IRRRB, which owns the land, received emergency funding to pay for the repairs.

Opponents of copper-nickel sulfide mining in northeastern Minnesota — like the proposed PolyMet open pit mine near Hoyt Lakes — are pointing to the incident as a cautionary tale.

"Unfortunately, I'm not surprised," said Bridget Holcomb, a volunteer with Duluth for Clean Water, an advocacy group that has formed in opposition to the PolyMet proposal. "There are mine accidents, spills, breaches like this all the time, and often they don't reach the public."

Dirt dams like the one at the Hector Mine are vulnerable to failure from heavy rainstorms or runoff, said Paula Maccabee, advocacy director for Water Legacy, which opposes sulfide mining.

"This gives us a very small thumbnail print of what can happen when a dirt dam breaches and pollution spills forth," she said.

Minnesota requires that mining companies provide financial assurance to cover future environmental cleanup costs. But Maccabee said that doesn't cover catastrophic spills or dam breaches.

"It's not uncommon for a mine to have waste spill out afterwards, and have no one but the public holding the bag," she said.

Meanwhile, officials in Biwabik say they'll continue to monitor the affected lakes throughout the summer.