Gov. Mark Dayton on Wednesday vetoed a bill that would have killed a state pollution rule designed to protect wild rice, calling it an extreme overreach by state lawmakers and a violation of the federal Clean Water Act.

Dayton said the Legislature has 12 days to come up with another proposal “that respects federal law and protects our precious wild rice and waters.”

The bill, passed by the Republican-controlled House and Senate, was the latest in a nearly 10-year political and legal battle over Minnesota’s official state grain. At issue is a state standard governing water quality and sulfate, a mineral salt that is hazardous to wild rice and is produced mainly by mining operations and wastewater treatment plants.

Though the state law applies only to wild rice, which in the United States grows almost exclusively in Minnesota, sulfate can also damage other aquatic plants, and it plays a critical role in the transfer of mercury from the environment into the food chain, including game fish that people eat.

Republican lawmakers and business leaders said the bill was necessary to provide “regulatory certainty” to Minnesota industry and expressed disappointment in the governor’s decision.

“The governor vetoed a bill that’s important to all of Minnesota,” said Rep. Dale Lueck, R-Aitkin. “We can’t continue to push this standard from 1973 that’s never been in effect and [would] cost billions of dollars and destroy our local communities.”

Still, Lueck and other supporters of the bill said they would work with Dayton and other groups to find a workable solution. “We must solve these problems without harming our natural resources or creating regulatory conflicts,” said Emil Ramirez, District 11 director of the United Steelworkers.

Environmental groups praised the veto, and they too expressed hope that the state could reset its protection of wild-rice waters and perhaps find new technologies to solve the problem for industry while not endangering water quality.

“We can continue to bicker over what the sulfate standard should be, or we can admit that the most popular option would be to find a solution that works for everyone,” said Paul Austin, executive director of Conservation Minnesota.

Others were not so optimistic. Nancy Schuldt, environmental director for the Fond du Lac Band of Chippewa, fears the fight over wild rice has become so polarizing that compromise has become impossible.

After years of research conducted at the direction of the Legislature, the Minnesota Pollution Control Agency (MPCA) last year finalized a new water quality standard for sulfate, only to see it overturned recently by an administrative law judge. The judge said the new rule was too complicated and unconstitutionally vague. But she upheld the state’s previous standard, 10 parts per million, which has been on the books since the 1970s.

‘An impossible bind’

In his veto letter to legislators, Dayton agreed that the standard was difficult to implement because of its cost, and that the state’s research found that, in some waters, the concentrations of sulfate can be higher without killing wild rice. Sulfate’s effect on wild rice is highly influenced by the chemistry of the water and muck where it grows.

The Legislature’s bill would have required the MPCA to start over on a new rule, which the agency planned to do anyway because of the administrative ruling, and it provided $500,000 for research and projects to promote the health and growth of wild rice.

But it also dismissed the scientific research behind the agency’s latest proposed standard, and it would have prohibited the MPCA from enforcing the prior standard while it conducts another multiyear round of rule-making.

Dayton said that step would violate the federal Clean Water Act, put the agency in an “impossible bind,” and inevitably lead to litigation. “Some legislators have decided … that they do not like the science. In response, they have attempted to abolish the standard and pretend that it solves the problem,” he said in his letter to legislators.

Last week, Dayton had asked the Legislature to work with his administration on another plan for wild rice protection. Instead, both the House and Senate brought the bill to a vote, with supporters citing the need for regulatory clarity. Republicans also fumed that Dayton recently refused to meet with a coalition of supporters of the bill. Instead, Lueck said, Dayton’s staff met with them and “ended the meeting by announcing the governor had decided to veto the bill.”

Because it affects a key Minnesota industry and a beloved state grain, the sulfate rule has been an incendiary issue for years, leading to lawsuits, multiple legislative efforts to circumvent the federal rules and millions of dollars in new research.

Though the standard has been in state and federal law for decades, it was largely ignored until several Minnesota Indian tribes and environmental groups asked the U.S. Environmental Protection Agency to compel its enforcement in the early 2000s. Since then, the EPA has pressed Minnesota regulators to incorporate the standard in permits for taconite mines and in the state’s environmental review for PolyMet Mining, the proposed copper-nickel mine near Hoyt Lakes. PolyMet’s permit to mine, which is now under final review by state regulators, would require water treatment for decades at a cost of hundreds of millions of dollars, in large part to remove sulfate water discharged by the mine and its operations.