As required by the federal Clean Water Act, the MPCA assesses all waters of the state and creates a list of impaired waters every two years. This list includes waters that fail to meet water quality standards and uphold that water body’s designated use.
The listings are based on intensive water quality monitoring of major lakes and streams in Minnesota’s 80 watersheds, along with data from partners. This list is used to set pollutant-reduction goals needed to restore impaired waters, called the total maximum daily load (TMDL).
Approved by U.S. EPA in April 2024, Minnesota's list includes the Total Maximum Daily Load (TMDL) list (303(d) list); 2024 Inventory of all impaired waters; delisted waters; changes and corrections from the 2022 list; Appendix A of the Statewide mercury TMDL.
- Approved by U.S. EPA - April 2024
- Impaired waters viewer (IWAV)
The guidance manual describes Minnesota's monitoring and assessment strategy, assessment tools, and the assessment process. This guidance defines the required data and information and lays out the criteria by which waterbodies are assessed to determine if beneficial uses are supported or impaired.
Defining impaired waters
A body of water is considered “impaired” if it fails to meet one or more water quality standards. Minnesota water quality standards protect lakes, rivers, streams, and wetlands by defining how much of a pollutant can be in the water before it is no longer drinkable, swimmable, fishable, or useable in other, designated ways (called “beneficial uses”). It is important to note that a water impaired for one designated use does not mean it cannot be used for other designated uses.
Impairments include:
- Mercury levels that lead to limits on fish consumption
- Nutrients that grow algae
- Sediment that clouds water
- Bacteria that can make water unsafe for swimming
- Unhealthy conditions for fish and bugs
- PFOS found in fish tissue
- Sulfate impairments that may hinder the biological production of wild rice
The MPCA works with many partners to identify the sources of pollutants and stressors to aquatic life, and determine reductions in pollutants and other changes needed to restore waters to meet water quality standards.
Other information
MPCA uses this biennial narrative report to meet some of the reporting requirements under the federal Clean Water Act.