Minnesota's impaired waters and TMDLs
The federal Clean Water Act requires states to adopt water quality standards to protect lakes, streams, and wetlands from pollution. The standards define how much of a pollutant (bacteria, nutrients, turbidity, mercury, etc.) can be in the water and still meet designated uses, such as drinking water, fishing, and swimming. A water body is “impaired” if it fails to meet one or more water quality standards.
To identify and restore impaired waters, Section 303(d) of the Clean Water Act requires states to:
- Assess all waters of the state to determine if they meet water quality standards.
- List waters that do not meet standards (also known as the 303d list) and update every even-numbered year
- Conduct TMDL (total maximum daily load) studies in order to set pollutant reduction goals needed to restore waters.
Federal and state regulations and programs also require implementation of restoration measures to meet TMDLs.
MPCA responsibilities include monitoring and assessing water quality, listing impaired waters, and conducting TMDLs in Minnesota. The agency also coordinates closely with other state and local agencies on restoration activities. Monitoring suggests that about 40 percent of Minnesota's lakes and streams are impaired for conventional pollutants, a rate comparable to what other states are finding. Impaired waters identified through the assessment process are placed on the Impaired Waters List. More information is available on the MPCA Web site about environmental monitoring and water-quality standards.
To best align resources, the MPCA is following the Intensive Watershed Monitoring approach for both monitoring (agency and local via grant funds) and assessments.
The Clean Water Legacy Act, passed in June 2006, allocates first-year funding to accelerate water monitoring, TMDL development and restoration activities throughout the state. The Clean Water Council was established by the Legacy Act to provide recommendations on the administration and implementation of the Act.
Assessment and listing documents
- Assessing and Listing Impaired Waters Fact Sheet
- Guidance Manual for Assessing the Quality of Minnesota Surface Waters for Determination of Impairment 305(b) Report and 303(d) List — 2014 Assessment Cycle
- Natural Background and Water Quality — Guidance document for assessment of aquatic life use support
- Guidance for considering natural background when assessing lakes for eutrophication
The MPCA provides access to assessment-related water quality information through its Assessment Water Quality viewer.
Links to related sites
- U.S. Environmental Protection Agency, Office of Water: Total Maximum Daily Load (TMDL) Program
- Minnesota Governor's Clean Water Initiative, Clean Water Cabinet
- Minnesota Department of Agriculture, Impaired Waters Program
- Minnesota Board of Soil and Water Resources
- Minnesota Department of Natural Resources