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305b Assessments of Lake Conditions in Minnesota's Major River Basins

Lake assessments are prepared for the U.S. Congress under Section 305b of the Clean Water Act to:

• estimate the extent to which Minnesota waterbodies meet the goals of the Clean Water Act, and
  
  
• share this information with planners, citizens and other partners in basin planning and watershed management activites.

These assessments are a fundamental part of MPCA's state water quality management program.

Lakes are assessed for the swimmable goal of the Clean Water Act. Categories of assessments for supporting swimming use are:

• fully supporting (FS)
• partially supporting (PS)
• not supporting (NS)

Information about how these assessments are made is available at: Lakes Assessment Process and Methods.

To view assessments of specific lakes, use the Lake Water Quality Assessment Program Data Search.

To view assessments of lakes, select the major river basin from the list of files shown below. Within each major river basin table, lakes are grouped by major watershed. These assessments are based on data collected through 2004.

Basins in Minnesota

Minnesota Ecoregions Map

Basin Reports

• 2008 Integrated Report: Surface Water Section (Abbreviated Narrative Report) - Report to the Congress of the United States: Water Years 2004-2005. This report integrates 305b assessments, which measure attainment of standards for fishable and swimmable waters, and 303d (TMDL) listings of impaired waters. Assessments are organized by basin for the entire state and the report also presents statewide summaries. The report describes Minnesota's monitoring and assessment strategy, assessment tools, and the integrated assessment process. It also briefly describes the state's response to these assessments in terms of development and implementaion of TMDLs and special state strategies.

Lake Assessments

Please note that the interative maps below will open in a new browser window. For the interactive maps to work best, your computer should:

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Basin	Basin Reports	Maps
Cedar and Des Moines River	Minnesota Lake Assessments Cedar River - Aquatic Recreation Use Minnesota Lake Assessments Des Moines River - Aquatic Recreation Use	Cedar River Basin for Swimming Cedar River Basin for Aquatic Consumption Des Moines River Basin for Swimming Des Moines River Basin for Aquatic Consumption
Lake Superior	Minnesota Lake Assessments - Aquatic Recreation Use	Lake Superior River Basin for Swimming Lake Superior River Basin for Aquatic Consumption
Minnesota River	Minnesota Lake Assessments - Aquatic Recreation Use	Minnesota River Basin for Swimming Minnesota River Basin for Aquatic Consumption
Missouri River	Minnesota Lake Assessments - Aquatic Recreation Use	Missouri River Basin for Swimming Missouri River Basin for Aquatic Consumption
Rainy River	Minnesota Lake Assessments - Aquatic Recreation Use	Rainy River Basin for Swimming Rainy River Basin for Aquatic Consumption
Red River	Minnesota Lake Assessments - Aquatic Recreation Use	Red River Basin for Swimming Red River Basin for Aquatic Consumption
St. Croix River	Minnesota Lake Assessments - Aquatic Recreation Use	St. Croix River Basin for Swimming St. Croix River Basin for Aquatic Consumption
Upper Mississippi, Lower Portion	Minnesota Lake Assessments - Aquatic Recreation Use	Upper Mississippi River Basin, Lower Portion for Swimming Upper Mississippi River Basin, Lower Portion for Aquatic Consumption
Upper Mississippi, Upper Portion	Minnesota Lake Assessments - Aquatic Recreation Use	Upper Mississippi River Basin, Upper Portion for Swimming Upper Mississippi River Basin, Upper Portion for Aquatic Consumption

Lakes Assessment Process and Methods

Minnesota lake assessments focus on trophic state and its relationship to support of designated uses, specifically swimming and aesthetics. Carlson's Trophic State Index (TSI) was used to combine measures of summer Secchi Disk transparency and epilimnetic concentrations of chlorophyll-a and total phosphorous. The TSI values are calculated as follows:

• Secchi disk (SD)
  TSI (TSIS) = 60 - [14.41(natural log)(Secchi average)]
• Total phosphorus (TP)
  TSI (TSIP) = [14.42 (natural log)(TP average)] + 4.15
• Chlorophyll-a (chl-a)
  TSI (TSIC) = [9.81(natural log)(chl-a average)] + 30.6

(TP and chl-a in micrograms per liter (ug/L) and SD transparency in meters).

The index ranges from 0 to 100 with higher values indicating more eutrophic conditions. The TSI values were calculated for each variable, then averaged for each lake (Figure 1).

Figure 1. Carlson's Trophic State Index (TSI)

Table 1 provides the Trophic State Thresholds used for determining use support for lakes. Actual detail of the assessment process for 303(d) and 305(b) may be found in the 2004 Minnesota Water Quality Surface Water Section report.

Table 1. Trophic Status Thresholds for Determination of Use Support for Lakes
(Carlson’s TSI noted for each threshold. Taken from guidance manual.)

Thirtyfour years of data (1970-2004) were used in the assessments. Lakes sampled within the last 10 years are reported as "Monitored", compared with "Evaluated" when assessments are based on monitoring data more than 10 years old. All data are stored in the U.S. Environmental Protection Agency (EPA) "STORET" data system.

Lakes for which no monitoring data were available may have been assessed using a survey of local resource managers, as described below.

Map Shapefiles

The zipped (compressed) file below contains a shapefile which represents the Minnesota 2008 lake assessments (per Section 305(b) Clean Water Act). These files were created for those interested in preparing computerized maps of the 305(b) lake assessments. To use these files you will need Geographic Information System (GIS) computer software. The zipped file contains a shapefile and metadata for aquatic consumption and aquatic recreation use support for lakes. The projection for the shapefile is UTM extended zone 15, NAD83. The shapefile was created by the Minnesota Pollution Control Agency using the 1:24,000 scale National Hydrography Dataset. If you have any questions or comments, please contact Carrie Bartz at 651-757-2214

Map Shapefile of Minnesota 2008 Lake Assessments (file size = 16 MB)

More Information

For more information about the 305b assessments of lake conditions in Minnesota's major watersheds, contact Steve Heiskary at 651-757-2419.