Environmentalists warn that manure spills are putting Wisconsin's water supply at risk and that the proliferation of so-called "megafarms" will lead to more pollution accidents.
Livestock operations have spilled at least 4.8 million gallons of manure since 2009, according to Wisconsin Department of Natural Resources data and published reports across Gannett Wisconsin Media.
More than 3 million gallons of manure spilled in 2013 and 2014. The numbers could be even higher because the DNR's records don't include cases that are still under investigation by the agency.
DNR records show most of the incidents resulted from equipment malfunctions, such as ruptured hoses, or accidents, including manure trucks that tipped over.
Most spills are cleaned up without any measurable harm to people or animals, DNR spokesman Ed Culhane said. But at least some have caused fish kills, polluted wetlands and contaminated drinking water, according to reports published by Gannett Wisconsin Media.
Environmental advocacy groups say pollution from liquified manure is one of the biggest hazards for Wisconsin's drinking wells and waterways.
"As a farmer, I've watched some of these issues. Manure is literally running into ditches and getting washed into rivers," said Lynn Utesch, co-founder of Kewaunee C.A.R.E.S., a group promoting environmentally friendly farming practices.
Manure is liquified by using water to flush animal waste from barns into storage lagoons. The manure is then sprayed on fields as fertilizer using trucks or irrigation systems.
Leaders in the dairy industry say liquid manure is safe when managed properly. The DNR has strict regulations for large farms that produce the most manure, including limits on when and how much can be sprayed.
"We're way ahead of the game (with manure management) compared to the rest of the nation," said Laurie Fischer, director of dairy policy for the Dairy Business Association.
But critics argue accidents are becoming larger and more frequent.
Manure contains many pathogens, including E. coli and coliform bacteria, that can harm people and animals. When liquified, the manure more easily flows into waterways or seeps into groundwater, said Jason Lowery, spills response team leader for the DNR.
Areas in central and northeastern Wisconsin are particularly vulnerable to contamination because of sandy and rocky soils that allow liquids to seep through more easily and quickly, DNR officials and local conservationists said.
A growing number of conservationists, landowners and lawmakers are blaming the spills and well pollution on the proliferation of large farms.
Wisconsin is home to more than 260 of such farms, also called concentrated animal feeding operations. That's up from less than 50 just 10 years ago, according to DNR permitting records.
These farms are home to about 400,000 dairy and beef cows that produce 47 million gallons of manure every day, based on estimates by the U.S. Environmental Protection Agency. That's more waste than the amount produced by all the residents of Wisconsin combined.
"When you have one farm producing millions of gallons of manure in one year and there's a need to spread that over massive areas — I just have to think the danger is greater," said Shahla Werner, director of the Sierra Club's Wisconsin John Muir chapter.
Fischer, of the Dairy Business Association, said it's unfair to blame the large operations, which are becoming increasingly necessary for farmers to make a living and meet people's demand for food.
"Regardless of if you're a small, medium or large farm, accidents can occur. It's how we manage those farms on a day-to-day basis that matters," she said.