State and local officials are working on a plan they say could improve water quality on Lakes Winona, Agnes and Henry while easing some regulatory pressure on the sewer plant in Alexandria.

"It's well worth trying the new approach and we could be a model for the rest of the state," said Sen. Torrey Westrom, author of a bill to allocate $600,000 to aid the plan.

The plan does something not tried before in Minnesota, officials say, which is to allow the Alexandria Lake Area Sanitary District to get some relief from having to meet phosphorus levels it discharges in exchange for removing phosphorus from the lake. The Minnesota Pollution Control Agency would have to sign off on the plan, which sewer chief Bruce Nelson says it has not yet done.

The sewer plant would have to remove 2.6 pounds of phosphorus from the lake in exchange for every 1 pound of leeway it would get in its operating permit. Excess phosphorus can spur algae growth on lakes.

How to deal with pollution in Lake Winona has vexed officials for more than a decade. The sewer plant discharges directly into it, and while the modern plant has drawn praise from some environmentalists, Nelson says the lake still suffers from sewage piped into it from early in the 20th century. Winona sends polluted water downstream to Agnes and Henry.

Compounding the problem is carp, an invasive fish that stirs up phosphorus from lake bottoms.

Officials would remove phosphorus by bringing in commercial fishermen to use nets to remove carp in summer and winter, then turn the fish into a product like fertilizer, Nelson said. They would then erect traps to prevent carp from migrating into the chain of lakes. Officials would spread alum in Lake Agnes to bind to the phosphorus, sinking it to the bottom where it would be rendered inert.

"Obviously we've been talking about this issue for a long time," said Marty Schultz, city administrator for Alexandria. "It's exciting to at least see there's a possibility for some funding and for starting to look at plans to address the issue."

The Minnesota Center for Environmental Advocacy, an environmental group that sued the state in 2012 for allowing pollution in Lake Winona, said it had not had time to explore the plan.

Spokesman Aaron Klemz said the group has been busy fighting efforts at the state capitol to relax requirements for sewer plants around the state. It would oppose more lenient standards in an operating permit, he said.

"It seems like alum treatments and carp treatments could be beneficial," Klemz said. "But we're skeptical that they should result in a change to the permit itself."

He added that although carp can stir up phosphorus, they're not the root cause of the pollution. "Ultimately the reason why there's a problem is because those nutrients exist in the lake," Klemz said.

If this plan doesn't work, sewer customers could be on the hook for a much more expensive option, $14 million in upgrades to further reduce the amount of phosphorus it sends into Lake Winona.

"Everyone is sensitive to the environment but everyone is also sensitive to their monthly bills," Westrom said. "There has to be a balance here. ... That seems to be a smart way to go and a good use of taxpayer dollars and save the ratepayers money."