The state will add Dane County’s chain of lakes to its list of “impaired waters” because of heavy nutrient pollution from surrounding farmland that causes unnatural weed growth and nasty-smelling algae blooms, state officials said Friday.

Dane County officials expressed concern that the listing of the four Yahara lakes — Mendota, Monona, Waubesa and Kegonsa — might upset or undermine extensive cleanup efforts already underway in cooperation with local farmers. It would be the first time the lakes landed on the state list because of nutrient pollution.

“Being listed as impaired brings a lot of negative attention,” said Melissa Malott, executive assistant to County Executive Joe Parisi. “We are working with the farmers as never before. I don’t understand exactly why (the state) would be doing this now.”

But the listing also could add further urgency to efforts to prevent farm manure from running off fields and into streams and lakes, said Josh Wescott, Parisi’s chief of staff.

The lakes will be placed in a category of the impaired waters list that acknowledges plans are in place that will reduce phosphorus levels to meet standards, said Wisconsin Department of Natural Resources impaired waters list coordinator Aaron Larson.

The lakes exceed exacting new phosphorus levels that were established in 2010. The listing is part of a federally mandated update that takes place every two years, Larson said.

Standards and testing methods have changed several times since Wisconsin’s first impaired waters list was approved in 1998, so it’s difficult to pinpoint the extent to which an actual increase in phosphorus caused the listing, Larson said.

The entire Rock River basin, which includes the Yahara lakes, will also be listed, Larson said. Other parts of the basin had been identified previously, he said.

The new list will include 703 bodies of water that don’t have an adequate cleanup plan and 152 that do, Larson said.

Dane County has in place a variety of cleanup initiatives — including planting vegetation on stream banks to reduce erosion, restoration of wetlands that slow runoff and measures to reduce improper spreading of manure on farm fields.

The county has budgeted more than $5 million in 2014 for improved manure storage and treatment, acquisition of vulnerable stream banks and land along waterways, grants to reduce urban runoff and other measures, Wescott said.

Many of the measures are accomplished through cooperative agreements with farmers and others, Wescott said.

However, last spring heavy rains and snowmelt atop frozen soil swept an unusually large amount of nutrient-rich manure into the water, so the county toughened its ordinances after consulting with farmers, he said.

Starting Jan. 1, farmers who spread manure in the winter may be hit with increased fines of up to $600 a day for repeated violations of ordinance provisions requiring certain precautions to prevent pollution. The ordinance change also requires farmers to renew winter spreading permits every three years. The permits have been valid indefinitely.

Wisconsin’s growing dairy farms produce millions of gallons of manure that often is stored in lagoons because sometimes the ground is too wet for vehicles to operate in fields, and at times when spreading poses the highest risk of runoff that can kill fish and foul lakes.

However, storage facilities, including those at manure digesters, can fail. Two spills from large storage tanks in the Lake Mendota watershed this year each released 300,000 gallons of animal waste. Only one other Wisconsin manure spill in the past 15 years was larger, according to DNR records.

Analysis so far indicates a relatively small portion of each spill reached waters that flow into Lake Mendota, but safety measures are being reviewed, officials said.

The DNR establishes water quality standards and creates the impaired list for the U.S. Environmental Protection Agency.

Lakes in the Yahara chain have been listed because of other pollutants, such as mercury and PCBs, according to the DNR website for impaired waters.

Lake Wingra, which drains into Lake Monona, is listed for phosphorus and PCBs. Several Madison beaches have been listed for bacteria.

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