Relentless rains this month have caused 17 manure pits at 15 large farms in southwestern Minnesota to overflow, releasing livestock waste into the environment.

The overflows, all at open pit lagoons, happened in Rock, Nobles and Jackson counties, said Andrea Cournoyer, a spokeswoman for the Minnesota Pollution Control Agency (MPCA). The agency is working to monitor and mitigate any potential damage from the spills, she said.

High concentrations of manure can be dangerous to human health and can cause fish kills and threaten water quality even after floodwaters recede. But the manure in the basins overflowing from the extreme rainfall is heavily diluted, said Randy Hukriede, feedlot program manger for the MPCA. None of the basins that overflowed contained pure manure.

"When these do overflow the solids and things collected tend to settle out," he said. "Generally speaking, when we're dealing with very, very dilute material like this, we haven't received reports of any fish kills or things like that."

The overflows have so far been contained to nearby farm fields, and none of the 17 overflowing pits have directly discharged into a river or stream, Hukriede said.

The state's largest feedlots, which include dairies and pig and turkey operations that have roughly 1 million pounds of total livestock or more, are required to report any manure overflows to the state. There are about 1,000 feedlots of that size in the state. State regulators ask smaller farms to report overflows as well, but they are not required to.

Hukriede said the agency is working with the flooded feedlots to mitigate spillage. That can be done by diverting manure onto a dry enough field, or finding a storage basin that has room, or building up berms and sealing culverts.

"This is a big challenge right now, you might imagine, because there has just been so much precipitation that a lot of these options are off the table," he said.

Glen Stubbe
Video (00:44) Walz and Klobuchar toured flooded areas in a Minnesota National Guard helicopter, traveling over LeSueur, Henderson, Mankato and Waterville.

Thom Petersen, the Minnesota Department of Agriculture Commissioner, viewed the flooding in southern Minnesota by helicopter on Tuesday afternoon.

"Those feedlots [with overflows] are working closely with the Minnesota Pollution Control Agency and did not discharge into bodies of water but rather out into fields," he said.

Peter Bakken, a rancher who operates a feedlot in Rock County, said the heavy rains have put his manure storage facility at the brink of overflowing.

He said it's the second time since securing his permit that he's had to phone into the state to report a potential overflow because of flooding. He and his family get their drinking water from the property, he said, and potential manure pollution is one of a host of complications the historic rain has caused farmers in the area.

"We build for a 100-year flood," Bakken said. "And we get 100-year floods every other year it seems."

Minnesota Department of Health officials warned that contamination from both animal and human waste is one of many reasons people need to avoid floodwater.