Lake monitoring

Lake monitoring tools

Because lakes are central to Minnesota's economy and our way of life, it is imperative that we maintain or improve their water quality. The Minnesota Pollution Control Agency (MPCA) monitors and assesses lakes throughout the state to make sure they meet water quality standards. The MPCA and its partners (soil and water conservation districts, watershed districts, tribal entities, and non-profit groups, and citizens) all play a role in keeping our lakes healthy.


The MPCA uses three strategies to monitor the water quality of Minnesota's lakes:

In addition to its routine lake monitoring activities, the MPCA also participates in special studies, such as the Minnesota Department of Natural Resources' Sentinel Lake program and in the EPA's National Lake Assessment Projects.


The MPCA's lake monitoring goals are tied to the goals of the 1972 Clean Water Act for restoring and protecting the multiple beneficial uses and ecological integrity of America's waters.

Primary goals:

  • determine if lake water quality supports recreational activities such as swimming, wading, and boating.
  • measure and compare regional differences in water quality.
  • identify long-term trends in water quality.

Monitoring strategy

By 2006, only a small percentage of Minnesota's lakes had been monitored for basic water quality. The MPCA decided it needed to examine more lakes at a faster rate, and developed what it calls the watershed approach.

The MPCA uses a 10-year cycle of intensively monitoring an average of eight watersheds a year. This monitoring includes lake water chemistry, and stream chemistry and biology, such as fish populations. The resulting data help determine if lakes meet the standards for public health, recreation and aquatic life. This watershed approach allows the agency to examine more lakes at a faster rate. The first 10-year watershed cycle began in 2008 and will end in 2017.

Monitoring design

Routine lake sampling occurs once per month from May through September for a period of two years. The primary focus is on collection of total phosphorus (nutrient), chlorophyll-a (pigment in algae), and Secchi depth (water clarity). With this information, the MPCA can determine the condition of the lake, commonly referred to as the “trophic status.” It is not possible to sample every lake in every major watershed in Minnesota. The goal is to monitor and assess all lakes larger than 500 acres, and at least 50% of smaller lakes. The MPCA’s staff and local partners ensure a good mix of large and small lakes represent a given watershed.

Nutrient levels drive the productivity of the lake. An increase in nutrients often leads to an increase in plant or algal growth and a decrease in water clarity. In general, high nutrient levels increase the likelihood that nuisance algal blooms will grow and that lakes will not meet aquatic recreational uses. However, sometimes other factors play a role. For example, some lakes are naturally a tea color that can decrease water clarity regardless of nutrient levels. For this reason, staff also collects data on water color, clarity, temperature and other parameters. Measurements include in-field measurements and lab analysis.

The in-field measurements include:

  • pH
  • temperature
  • conductivity
  • dissolved oxygen
  • oxidation reduction potential (ORP)
  • Secchi transparency

The laboratory measurements include:

  • total suspended solids (TSS)
  • suspended volatile solids (SVS)
  • total phosphorus (TP)
  • total Kjeldahl nitrogen (TKN)
  • nitrite-nitrate (NO2+NO3)
  • total organic carbon (TOC)
  • chlorophyll-a
  • pheophytin-a
  • chloride
  • alkalinity
  • hardness (May only)
  • sulfate (May only)

The MPCA uses the following standard operating procedure (SOP) when conducting its lake monitoring, and also requires Surface Water Assessment grantees to use this procedure:


The MPCA gathers water quality data from its staff, citizen volunteers, and partners, and then uses the data to assess the condition of Minnesota lakes. This assessment focuses on whether the water meets standards to protect recreational uses such as swimming. Visit the MPCA's Environmental Data Access webpage to see lake quality data and assessments for individual lakes.

Starting in 2008, the MPCA began a 10-year cycle for examining major watersheds or drainage areas. The MPCA is meeting its goals to study all 80 major watersheds within 10 years, with 17 watershed assessments completed. An additional seven watersheds will be assessed 2012, with the remaining watersheds scheduled through 2019. More detailed information for individual lakes and stream sections can be found on the MPCA's Environmental Data Access web page.

The MPCA, with the help of state and local partners, uses data from the intensive watershed monitoring to determine which lakes are healthy and need protection, and which lakes are polluted and need restoration.

Once assessments of basic water quality have been made, the monitoring data gathered during intensive monitoring serve as a starting point in determining the sources and magnitude of pollution for polluted waters, or as a baseline to set protection measures for those waters that are not polluted. State agency and local colleagues are partnering to conduct intensive monitoring, assess the resulting monitoring information, and to develop restoration and protection plans. Through the Watershed Approach, intensive sampling and assessment of lakes and streams in all 81 major watersheds allows for better protection of Minnesota’s clean lakes, and restoration of the polluted ones.

Percent lakes fully supporting aquatic recreation

Minnesota map showing percent lakes fully supporting aquatic recreation

Data and reporting

After assessing water quality data and determining if waters support recreational uses, the MPCA publishes its findings in detailed reports. The MPCA has written hundreds of these reports since 1985. More recent reports cover major watersheds instead of individual water bodies. In addition to reporting on lake assessments, the MPCA also publishes regional and trend studies.

Below are some of the MPCA's recent lake assessment reports. Following the list is a spreadsheet of all available water quality reports, sorted by county. The spreadsheet includes the name of the lake, the Minnesota Department of Natural Resources lake identification number, the year the study was conducted, and the type of report.

Report title

Year study conducted

PDF icon CLMP+ Report on Grass Lake (Anoka County)


PDF icon CLMP+ Report on Pike Lake (St. Louis County)


PDF icon Assessment Report of Selected Lakes within the Buffalo River Watershed Red River of the North Basin


PDF icon Water Quality Assessments of Select Lakes within the Mississippi River (St. Cloud) Watershed


PDF icon CLMP+ Report on East Sunburg Lake (Kandiyohi County)


PDF icon CLMP+ Report on Sunburg Lake


PDF icon CLMP+ Report on Star Lake (Meeker County)


PDF icon CLMP+ Report on Lewis Lake (Kanabec County)


PDF icon Assessment of Select Lakes within the Kawishiwi River Watershed (St. Louis, Lake, and Cook counties)


PDF icon 2010 Assessment of Selected Lakes in Cass County, McKeown Lake, Kid Lake, Kerr Lake, Lost Lake, Mann Lake, and Baby Lake


PDF icon Lake Cowdry, Stony Lake, North Union Lake, Taylor Lake — LAP Report 


PDF icon Assessment of Selected Lakes within the Sauk River Watershed (Douglas, Pope, Todd, Stearns, Meeker Counties)


PDF icon Assessment Report of Selected Lakes Within the Pomme de Terre River Watershed (Otter Tail, Grant, Douglas, Stevens, Swift, Big Stone Counties)


PDF icon Assessment of Selected Lakes within the North Fork Crow River Watershed (Pope, Stearns, Kandiyohi, Meeker, McLeod, Wright, Hennepin Counties)


PDF icon Assessment of Selected Lakes within the Le Sueur River Watershed (Blue Earth, Waseca, Faribault, Steele, Freeborn Counties)


PDF icon Assessment of Selected Lakes within the Little Fork River Watershed (St. Louis, Itasca, Koochiching Counties)


Office spreadsheet icon Additional lake assessment reports published prior to 2010 Please contact Lee Engel to request copies of old reports. 

< 2010

In addition to lake or watershed specific studies, a variety of research studies have been conducted as a part of MPCA’s lake water quality program. This research addresses specific issues such as the extent of blue-green algal toxins in Minnesota lakes, ecology and water quality of shallow lakes, determining lake trends based on sediment cores and providing support for development of lake eutrophication standards. Below are some of the more current studies that have been conducted. The spreadsheet that follows includes other reports developed as a part of lake water quality assessments.

Report title


PDF icon Historical Water Quality and Biological Change in Northcentral Minnesota Lakes


PDF icon Microcystin Levels in Eutrophic South Central Minnesota Lakes


PDF icon Developing Nutrient Criteria for Minnesota Lakes


PDF icon Interrelationships Among Water Quality, Lake Morphometry, Rooted Plants and Related Factors for Selected Shallow Lakes of West-Central Minnesota


Office spreadsheet icon Additional lake research studies published prior to 2009 Please contact Lee Engel to request copies of old reports. 

< 2009


The first 10-year cycle of sampling lakes and streams by watershed (the Watershed Approach) began in 2008, after two years of piloting the approach, and is scheduled to end in 2017. To date, monitoring plans are fully on track.

  • 35 major watersheds have been intensively monitored.
  • In 2012, monitoring began for 7 additional watersheds, and will be wrapping up in 2013.
  • In 2013, the MPCA and its local partners will begin monitoring eight more watersheds.

Intensive watershed monitoring

Intensive watershed monitoring map

Cumulative percent of watersheds completed chart

Cumulative percent of watersheds completed chart

Goals to assess the lake water quality data from intensive watershed monitoring are also on track.

  • To date, water quality data from 24 out of 80 major watersheds have been assessed.
  • An additional 11 watersheds will be assessed starting in February 2013, with the remaining watersheds scheduled for assessment through 2019.
  • The most recent lake assessments are shown below. More detailed assessment information for individual lakes can be found on the MPCA’s Environmental Data Access web page.

In 2018, a new watershed monitoring cycle begins, which means returning to the watersheds that were monitored 10 years earlier. Re-monitoring reveals if water quality has improved, declined, or remained the same.