Lake Biological Monitoring and Assessment

Program overview

The DNR Lake Biological Monitoring and Assessment (LBMA) program, in coordination with the Minnesota Pollution Control Agency (MPCA), surveys and evaluates the condition of aquatic life in lakes across Minnesota. These efforts are primarily funded by the Clean Water, Land, and Legacy Amendment through the Clean Water Fund and are implemented in alignment with MPCA’s watershed monitoring schedule. As part of this coordinated effort, the LBMA program recently completed a baseline report describing the condition of fish communities in 908 lakes in 47 watersheds across Minnesota.

Because Minnesota lakes vary widely in depth, complexity, temperature, productivity, and ecological setting, no single monitoring method can fully assess biological condition statewide. The LBMA program uses multiple complementary monitoring approaches designed to address the unique characteristics of different lake types and regions.

The program currently implements established monitoring methods while continuing to develop and refine additional approaches for specialized lake types. Together, these monitoring approaches provide scientifically defensible information used to assess aquatic life use, identify impairments, and guide protection and restoration efforts.

Fish-based index of biological integrity (IBI) monitoring

Click to enlargeFish IBI monitoring in lakes.

The fish-based index of biological integrity (IBI) monitoring approach evaluates lake health by examining fish community composition. By comparing the types and numbers of fish present to those expected under healthy conditions, this approach provides a measure of overall biological integrity.

Fish communities reflect long-term water quality and habitat conditions, as some species are sensitive to disturbance while others tolerate degraded environments. The fish-based IBI is used for Minnesota lakes throughout most of the state and plays a central role in aquatic life use assessments, impairment decisions, and lake management planning.

More information can be found on the Lake Index of Biological Integrity webpage.

Coldwater oxythermal habitat monitoring

Click to enlargeColdwater species and oxythermal habitat monitoring in lakes.

The coldwater oxythermal habitat monitoring approach evaluates whether lakes provide suitable temperature and dissolved oxygen conditions for coldwater fish species. These species require a narrow range of thermal and oxygen conditions that can be affected by nutrient enrichment, land use changes, and climate variability.

This method has been developed to assess stratified lakes capable of supporting coldwater species including Cisco, Lake Whitefish, and Lake Trout. It is currently undergoing review for formal incorporation into aquatic life use assessments. By assessing the availability and stability of cold, oxygen-rich habitat, this approach helps identify stressors that may not be fully captured through fish community data alone.

Boreal Shield fish community monitoring

Click to enlargeBoreal Shield fish community monitoring in lakes.

The Boreal Shield fish community monitoring approach is being developed specifically for lakes in northeastern Minnesota’s Boreal Shield region. Distinct from most other lakes in the state, these systems typically exhibit lower fish species diversity as a result of their geology, climate, surrounding landscape, and unique water chemistry characterized by soft water, low alkalinity, and natural tannin staining. In addition, many of these lakes occur within largely forested watersheds with relatively low levels of human disturbance, resulting in a limited disturbance gradient for developing and calibrating traditional assessment tools.

Because traditional fish-based IBIs are not well suited to these systems, this tailored monitoring approach is being developed to establish biologically realistic expectations for fish community condition. Once finalized, it will support accurate aquatic life use assessments and ensure that Boreal Shield lakes are evaluated using regionally appropriate benchmarks.

Assessment

Monitoring results are used by DNR staff to place lakes into one of four overall aquatic life use assessment categories: full support, non-support (impaired), inconclusive information, or insufficient information. Some lakes are also considered vulnerable if results suggest they are close to impairment. These assessments help guide lake management, restoration, and protection decisions for agencies, local governments, conservation groups, lake associations, and homeowners. Specific aquatic life use assessment decisions for lakes are also available in the MN Geospatial Commons.

Full support

Healthy lakes that support diverse, balanced fish communities and their respective habitat. These lakes are a priority for protection, and some restoration may also be recommended to maintain their condition.

Non-support (impaired)

Lakes that are degraded and where sensitive fish species typically no longer live. These lakes are a top priority for restoration, which can sometimes be extensive. These lakes are added to Minnesota’s Impaired Waters List.

Inconclusive information

Sampling produced enough data, but results were conflicting or very close to the impairment threshold, which prevented the ability to make a clear determination about the health of the lake. These lakes are frequently vulnerable to impairment.

Insufficient information

Sampling did not produce enough data to make a clear determination about the health of the lake.

Maps

Maps of watersheds assessed for aquatic life, based on the fish-based IBI in lakes. Each map illustrates the proportion of lakes within each watershed that fully supported aquatic life and the proportion that contained exceptional fish communities during the first round of monitoring and assessment.

Stressor identification

After assessment, DNR staff study stressors impacting the biological communities found in impaired and vulnerable lakes. Numerous stressors are considered during this process, but most often, the focus is on the impacts of water quality and shoreline habitat on the fish community. An overview of the many lake-specific stressors can be found in the stressors to biological communities in Minnesota lakes report. MPCA uses a similar process to identify stressors to biological communities in rivers and streams. For more information on stressor identification, go to the MPCA stressor identification webpage.

Stressor identification reports for both lakes and streams in watersheds that have been assessed can be found by navigating to the watershed of interest on the MPCA watershed information webpage or directly from the MN Water Research Digital Library. In some watersheds, stream and lake stressor identification reports are combined, and in others, they have been separated into two individual reports. Lake-specific stressor information for impaired or vulnerable lakes is also available in the MN Geospatial Commons.

LBMA program contacts

Learn more about Clean Water Land and Legacy Amendment funds and projects.