Amity Creek
Amity Creek is on the
impaired waters list for turbidity.

Follow this link to a GIS map of Restoration and Assessment activites in the region.

Understanding Impairments and TMDLs

The Clean Water Act (CWA) requires states to adopt water quality standards to protect waters from pollution. These standards define how much of a pollutant can be in the water and still allow it to meet designated uses.

Impaired waters are those waters that don't meet water quality standards for one or more pollutants.

Stream Science Symposium
February 2013

What is a TMDL?

A TMDL or Total Maximum Daily Load is a calculation of the maximum amount of a pollutant that a waterbody can receive and still meet water quality standards, and an allocation of that amount to the pollutant's sources.

Water quality standards are set by States, Territories, and Tribes. They identify the uses for each waterbody, for example, drinking water supply, contact recreation (swimming), and aquatic life support fishing), and the scientific criteria to support that use.

A TMDL is the sum of the allowable loads of a single pollutant from all contributing point and nonpoint sources. The calculation must include a margin of safety to ensure that the waterbody can be used for the purposes the State has designated. The calculation must also account for seasonal variation in water quality.

The Clean Water Act, section 303, establishes the water quality standards and TMDL programs. See USEPA, MPCA.

Learn about the MPCA's Biological Monitoring Program or watch a video about stream health


Read about the TMDL efforts underway for:

Maps showing the impaired streams in the Minnesota Lake Superior Basin:


National Info:

The Assessment Total Maximum Daily Load (TMDL) Tracking and Implementation System (ATTAINS) provides information reported by the states to the USEPA about the conditions in their surface waters.