FAIRMONT – The Minnesota Department of Natural Resources (DNR) recently released its 10-year fish monitoring report rating the health of Minnesota’s lakes, looking at over 900 lakes across 47 watersheds.

The test works by examining fish community composition through types and numbers of fish present compared to those expected under healthy conditions, in a type of monitoring called fish-based index of biological integrity (IBI).

“This is really looking at the overall health of the lake,” DNR Lake Biological and Monitoring Program Supervisor Jacquelyn Bacigalupi said. “It’s looking at the overall water clarity that supports a more diverse fish, plant and bug community, and how diverse and complex your habitat is. It really boils down to what people value. In many cases, people value clean water and a more diverse community, and that’s what this is measuring.”

The results of these tests do not, for example, attempt to measure the strength of lakes for fishing. Bacigalupi said that is a separate question outside of this program.

In looking at particular lakes, Bacigalupi said metrics were tailored to the lakes and the fish they historically have held.

“As you might expect, the fish that are in Martin County, the species that you sample might be a little bit different than if you’re in Itasca County,” she said. “We overlaid that with our resources that describe fish communities that should be present or were historically present based on major watersheds. Within the Mississippi watershed as opposed to the Minnesota River watershed or the Missouri River watershed, you’d have a different suite of species.”

The survey also looked at pollution in lakes through tolerant and intolerant species. Bacigalupi said it is actually better to have more fish of intolerant species than it is to have more fish of tolerant species, because it shows fish that cannot thrive with pollutants are able to have solid communities.

“A tolerant species is tolerant to anything that you throw at it, tolerant to pollution, and tolerant to eutrophication. An intolerant species would be one that’s intolerant to pollution. A fish IBI score is going to be higher if you have more intolerant species. A score is going to be lower if you have more species that are tolerant.”

This criterion is not one-size-fits-all, with the DNR looking specifically at the tolerant and intolerant fish species that have historically lived in a given lake and finding the populations of each.

“We have different models for different lakes in the different parts of the state,” Bacigalupi said. “Southern Minnesota lakes are not compared to lakes in northern Minnesota, and a deep lake is not compared to a shallow lake.”

Even so, compared to their projections, Fairmont’s lakes fell short of what the DNR was looking for. Out of a 0-100 score, of the four lakes in Fairmont’s chain of lakes that were tested (George Lake excluded), Sisseton got the highest score of 28, Hall scored a 20 and Amber and Budd Lakes scored a zero. Of the other lakes tested in Martin County, including Fox, Imogene, and South Silver, none got a score higher than 19.

This is not solely a Martin County issue. A majority of lakes across southern Minnesota tested under expectations. Across the region, 0 percent of lakes contained exceptional fish communities, and 25 percent of or less fully support aquatic life, according to the DNR’s map breakdown of their findings.

With Amber in particular, Bacigalupi said the fish community had six species that are considered tolerant. Of the five intolerant species previously found in this lake, which she said were types of minnows and shiners, none of them were still there.

On top of this, Bacigalupi said there was very high phosphorus and listed as impaired via eutrophication by the Pollution Control Agency.

“At the time this report was written, 86 percent of the contributing watershed was an unnatural land cover, including five active feed lots,” she said. “It also has a high dock density and a lack of submerged aquatic plants. You have green water, there’s no plants growing to support the fish communities.”

Given the amount of ground they had to cover across all of Minnesota, these reports were done at different times: Amber Lake was assessed in 2017; Sisseton Lake, the most recent, was assessed in Fairmont in 2023; and Bright Lake scored a 20 after being assessed last year.

Even so, with these results and relevant changes since the date of the survey, Bacigalupi said this data can now be used by the relevant authorities who work on the lakes to explore areas for improvement.

“The idea is that you could use the monitoring data that we’re providing to target implementation projects that either protect a lake, if that’s what it needs, or restore a lake. That’s done by other local units of government, not by the scientists on my team.”

For more information, visit the project page at dnr.state.mn.us/waters/surfacewater_section/lake_ibi/index.html.