Three groups representing dozens of Greater Minnesota cities said Thursday they will sue the state Pollution Control Agency (MPCA) to overturn or modify new water-quality rules meant to reduce phosphorus pollution in rivers, streams and Lake Pepin.

The cities contend that the new clean-water standards are excessive and will cost their communities millions of dollars to upgrade water and sewage-treatment plants. Phosphorus is found in human and animal waste and has been found to contribute to unwanted plant growth, including algae, in some of Minnesota's most treasured waterways.

"Everyone supports clean water," said Heidi Omerza, president of the Coalition of Greater Minnesota Cities. "But this time state regulators have gone too far."

Omerza and the heads of two other groups, the League of Minnesota Cities and the Minnesota Environmental Science and Economic Review Board (MESERB), said they will file their challenge Friday with the Minnesota Court of Appeals. They have argued for many months that the new state standards exceed federal limits, lack a basis in sound science and deserve additional peer review.

Agency officials declined to comment Thursday, saying they have not seen the suit.

In January 2014, an administrative law judge conducted a hearing on the proposed standards and issued a report that noted cities' concerns over the scientific basis for the change. But in May, the judge deferred to MPCA's expertise and recommended that the standards be adopted with only minor modifications.

The so-called nutrient standards for rivers and streams were adopted by the agency in June and not vetoed by Gov. Mark Dayton. The outstate cities pleaded for relief from the agency's Citizens Board, but were denied. Minnesota has had phosphorus standards for lakes since 2008.

Bob Van Moer, wastewater treatment plant superintendent in Marshall, said his city's plant discharges 2.5 million gallons of treated wastewater a day into the Redwood River, which flows into the Minnesota River and eventually Lake Pepin. If studies find the nutrient load in Lake Pepin to be excessive under the new standards, the state could require Marshall to reduce its phosphorus emissions.

Van Moer said a declaration of that kind would probably require significant reconstruction of the treatment plant at a cost of between $5 million and $10 million. "That would be a monster, financially," he said.

He added that two-thirds of the state empties into Lake Pepin one way or another and said cities like Marshall want more research to make sure the new restrictions will actually fix the lake's nutrient problem. The challengers fear that more expensive treatment plants won't produce an environmental benefit.

In the city of Moorhead, the state does not currently place a limit on phosphorus discharges into the Red River, where nutrient levels already are high from area farm runoff, said Bob Zimmerman, the city engineer. He said he's concerned about the new water quality standards because they give MPCA a new avenue to redesign the city's sewage treatment permit. If the plant had to remove phosphorus, costs would increase by up to $10 million over the next 20 years, he said.

"Up here on the Red, it doesn't do any good to set individual limits if everyone else is polluting the hell out of the river," Zimmerman said. "It would create an economic disparity for us here in Moorhead."

MESERB, the lead organization in the appeal, is a joint powers organization concerned with wastewater treatment and comprises several dozen Minnesota cities, including Rochester, St. Cloud, Mankato, Little Falls, Eveleth, Red Wing, Faribault, Northfield, Brainerd, Alexandria and Hutchinson. MESERB President David Lane said Thursday that the new standards will "seriously interfere with our obligation to provide high-quality treatment services at an affordable cost."

Tony Kennedy • 612-673-4213