(WLUK/AP) -- A state appeals court upheld a Calumet County judge's ruling that state regulators can force factory farms to obtain permits before they discharge pollutants.

Calumet County Judge Carey Reed ruled last year the state Department of Natural Resources has clear legal authority to protect the state's waters.

Wisconsin Manufacturers and Commerce, the state's largest business group, filed a lawsuit in Calumet County in May on behalf of the Wisconsin Dairy Alliance and the Venture Dairy Cooperative, two groups that lobby for factory farms.

The groups challenged the DNR's authority to impose mandates through factory farms' water pollution permits such as monitoring groundwater pollution levels, implementing manure management plans and limiting herd sizes. In 2023, the agency scaled back S&S Jerseyland Dairy's request to expand from roughly 5,000 cows to 10,000 cows, allowing the operation to add only about 2,400 animals.

The plaintiffs alleged that federal courts in 2005 and 2011 struck down the U.S. Environmental Protection Agency's authority to require factory farms obtain permits before they actually discharge contaminants into navigable waters. Therefore, the groups argued, the DNR's requirement that factory farms obtain permits before the fact was also invalid because it now conflicted with federal law.

The groups' interpretation would have allowed factory farms greater freedom to increase herd sizes and contaminate state waters with chemicals such as nitrates and phosphates from manure and other fertilizers.

Reed sided with the DNR, pointing to a section of state law that declares Wisconsin policy calls for restoring and maintaining the integrity of its waters to protect public health and aquatic wildlife.

The appeal challenged the DNR's authority to impose rules on large farms and the agency's definition of agricultural storm water discharge. In both cases, the appeals court found the rules were within the DNR's authority.

Clean Wisconsin and the Wisconsin Farmers Union, a group that lobbies for sustainable farming, joined the case as intervenors. Environmental law firm Midwest Environmental Advocates represented that group in the proceedings.