MN DNR Lake Monitoring
Every lake tells a story through its fish. The mix of species and their abundance can reveal the health of a lake and how the lake changes over time.
A new report from the Minnesota Department of Natural Resources, in partnership with the Minnesota Pollution Control Agency, documents that healthier lakes tend to have lower phosphorus from runoff or drainage, less disturbance of land in the watershed, and better shoreline habitat. The report compiles results from 1,444 fish-based index of biological integrity (IBI) surveys conducted between 2006 and 2025 for 908 lakes across 47 Minnesota watersheds.
“This report conveys the massive undertaking of more than a decade of studying fish populations specifically to assess the baseline health of lakes across the state,” said Derek Bahr, DNR fisheries research scientist. “Ultimately we can use these results to enable state and local partners to better protect, or if necessary, restore Minnesota’s aquatic habitats.”
Across these IBI surveys, the DNR sampled more than 3.7 million individual fish encompassing 89 different species, including 25 species that are considered intolerant to stressors and five that are considered species in greatest conservation need. Of the 808 lakes with sufficient data for assessment, DNR and MPCA staff found that 77% fully support aquatic life for fish biodiversity, and classified 23% as not supporting aquatic life for fish biodiversity, also called impaired.
Impaired lakes generally exhibited higher phosphorus concentrations, greater proportion of watershed disturbance, and lower shoreline habitat quality compared to lakes that fully support aquatic life. The MPCA uses IBI assessment data and recommendations from the DNR to formally decide whether to include lakes on a list of the state’s impaired waters. The latest report from the DNR conveys trends, whereas the MPCA issues separate reports on the impaired waters lists.
Lakes with exceptional fish communities had the highest shoreline habitat quality, and the lowest phosphorus and disturbance. Minnesota’s exceptional lakes also support more diverse, balanced food webs, and are significantly more likely to sustain naturally reproducing populations of cold-water species, species in greatest conservation need, and fish that anglers tend to seek out like muskellunge, northern pike, and walleye.
“This is great news to share on fish biodiversity in Minnesota,” said Leya Charles, impaired waters list coordinator for the Minnesota Pollution Control Agency. “Trend reports like this one show how many waterbodies are being protected, and that 77% of our state’s lakes assessed for fish biodiversity are meeting standards.”
The public and the agencies that serve them can use the results of the report in conjunction with related watershed-specific reports to inform efforts to protect all lakes, including the highest quality lakes, and to intervene with shoreline habitat or watershed management improvements for lakes that are on the verge of becoming impaired. They can also use these reports to help address stressors like shoreline development and nutrient runoff, with support from local partnerships. These partners often find cost-effective early interventions that preserve biological diversity and enhance recreational opportunities.
The report is available on the DNR’s lake biological monitoring and assessment webpage (mndnr.gov/waters/
Comments