WORTHINGTON — Representatives from the Minnesota Pollution Control Agency visited Worthington Thursday to train Des Moines River Watershed permitees about various factors impacting state standards.

Research scientist Matt Lindon outlined the history of water quality standards in the state. In 1973, Minnesota established standards for phosphorous content in lakes.

In 1991, the standards extended to chloride. The year 2008 brought lake-specific standards and, in 2015, MPCA expanded nutrient standards to Minnesota's rivers. Lindon noted that nitrogen standards are being prepared for future implementation.

Lindon explained that although most of the land comprising the Des Moines River watershed — which covers parts of Murray, Nobles, Cottonwood and Jackson counties, then extends across the Iowa state line — was originally prairie, 82% of current land use is agriculture. Land use is one major factor determining which nutrients accumulate in water sources, so it's a consideration when MPCA establishes standards.

Each watershed is given a health score between zero and 100 based on a number of factors. The Des Moines River Watershed has an average score of 47. Some positive factors are good impervious land cover, low soil erosion potential and few localized pollution sources. Challenges include perennial cover, feedlot pollution and phosphorous risk.

As an example, Lindon shared some data from Talcot Lake, just north of Dundee in Murray County. The state phosphorous standard for Talcot Lake is 90 milligrams per liter. The lake's latest phosphorous level was measured at an average of 408 mg/L — more than four times the standard.

Aerial photos going back to 1992 show how the lake and its surroundings have changed over time, revealing some clues about how certain nutrients enter the lake. One photo shows land erosion on the west side of the lake.

Another factor in the nutrient levels is inflow from upstream along the Des Moines River. There are five wastewater treatment plants upstream from Talcot Lake: Avoca and Iona, Currie, Fulda, Lake Wilson and Slayton.

One way to control nutrient contents in lakes and rivers is by establishing total maximum daily loads for each wastewater treatment plant.

"That's part of the balancing act we're trying to do here," Lindon said. MPCA does not want to overburden local entities with regulations, but it also has a responsibility to take care of the state's natural resources.

As the health of Talcot Lake improves, it will have a positive affect on other lakes downstream, like Heron Lake and Lake Okamanpeedan.

Lindon explained that data is collected from the watershed every 10 years over a two-year period. The data helps the MPCA re-evaluate the standards for each body of water in the watershed.

Project manager Katherine Pekarek-Scott added that as nutrient standards are revised, so are total maximum daily loads. She noted that the last set of standards was approved in 2008, so new total maximum daily load reports are being drafted at present and will be released to the public during spring 2020.

Once the public notice is published, Pekarek-Scott said, there will be a 30-day public comment period, during which anyone is welcome to submit a comment letter and/or petition MPCA to host a public information hearing or a contested case hearing.