MPCA Home > Water > Lake Monitoring

Lake Monitoring

Minnesota, the Land of 10,000 Lakes, actually has approximately 12,200 lakes greater than 10 acres in size. Monitoring and protecting the water quality of Minnesota lakes is one of the MPCA’s responsibilities.

In 1985, MPCA began monitoring and assessing the water quality of lakes, both individually and regionally. In 2006, lake monitoring activities at MPCA accelerated due to the passage of the Clean Water Legacy Act and the appropriation of additional lake monitoring funding. Currently, the MPCA monitors the water quality of approximately 100 lakes each year.
Lake characteristics vary by region: in the northeast, lakes tend to be deep, clear, and low in nutrients; in the south and western parts of the state, lakes tend to be shallow, nutrient-rich basins.

MPCA Lake Monitoring

The MPCA monitors approximately 100 lakes across the state each year, following the rotating watershed approach adopted by the MPCA in 2008. Each lake is sampled monthly from May to 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 (distance light will travel in water). With this information, it is possible to determine the condition of the lake, commonly referred to as the trophic status. 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 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, there are sometimes other factors at play that also must be considered (i.e., tea-stained lake water decreases lake transparency, independent of nutrient levels). For this reason, staff also collects information on water color, suspended solids, temperature, dissolved oxygen, and a number of other parameters. After a lake has been monitored for a minimum of two years, the water chemistry data are used to assess its condition. The water quality data and the results of the condition assessment are incorporated in a variety of products, including lake assessment reports, status and trend/update reports, and fact sheets.

The MPCA uses the following Standard Operating Procedure (SOP) when conducting its lake monitoring:

• SOP for Lake Water Quality Sampling

2009 Monitoring Schedule

The MPCA intends to monitor the following lakes during the 2009 field season:

• Lakes to be monitored in 2009

Citizen Lake Monitoring Program

In addition to monitoring lake water quality, the MPCA also coordinates the Citizen Lake Monitoring Program. Through this program, citizen volunteers make simple measurements of lake water transparency that help determine the condition of lakes.

Surface Water Assessment Grants

Local groups also monitor lake water quality. Since 2007, the MPCA has distributed Surface Water Assessment Grants to local partners, such as water conservation districts, watershed districts, and non-profit groups.  

Remote Sensing

Researchers from the University of Minnesota's (UMN) Remote Sensing Laboratory have been developing satellite-based approaches to monitor water resources. In 2003, Legislative Commission for Minnesota Resources funding allowed the MPCA and the UMN to partner on a project that paired citizen-collected Secchi disk data with Landsat satellite images to determine water clarity of all lakes across Minnesota greater than 20 acres in size. This partnership has continued with additional funding from the passage of the Clean Water Legacy Act. The MPCA uses this remote sensing information to assess lakes that are inaccessible or difficult to monitor repeatedly (e.g., lakes within the Boundary Waters Canoe Area Wilderness). For more information, please visit the Remote Sensing of Water Resources Web site.

Assessing the Condition of Minnesota Lakes

All of the water quality data from the MPCA’s monitoring activities, and those of citizen volunteers, other state agencies, and local groups are gathered together and used to assess the condition of Minnesota lakes. Lake water quality data are compared to state and federal water quality standards to determine if each lake is fully supporting or not supporting those standards set for recreational use (e.g., swimming, wading, etc.). Lakes not supporting aquatic recreational use are termed ‘impaired’ and are placed on a list biennially. A lake placed on the impaired waters list is required to be intensively researched through a Total Maximum Daily Load study to determine the source and extent of the pollution problem. The study also requires the development of a restoration plan.

Lake Water Quality Data

Water quality data collected by the MPCA, citizen volunteers and local group partners are stored in STORET, a federal repository for water quality data. This data can be viewed through two separate applications: the Lake Water Quality Summary database and the Environmental Data Access page.

Lake Reports

In addition to using MPCA, citizen and local group-collected water quality data to assess lake condition, the MPCA also analyzes this data for more in-depth studies of specific lakes, to assess water quality within a given region, to develop new water quality standards or for special studies. The analyses are then compiled into reports. 

Related Information

• Lake Finder - Minnesota Department of Natural Resources
• Aquatic Plant Management Program – Minnesota Department of Natural Resources
• EPA's Clean Lake Program