Working to protect the Mississippi River and its watershed in the Twin Cities area

Minnesota’s impaired waters 101

A very brief history of the Clean Water Act

In response to concerns regarding the health and safety of our nation’s waters, the Federal Clean Water Act (CWA) was signed into law in 1972.

Created to protect the “chemical, biological and physical integrity of our nations waters,” the CWA and subsequent revisions made groundbreaking changes to the way our nation monitors and protects our waters.

Clean Water Act Section 303(d)

(Summarized in plain English)

  1. States must assess all waters and determine if they meet H2O quality standards.
  2. Waters that do not meet those standards must be added to the Impaired Waters List (the 303[d] list). The list is updated biannually.
  3. States must conduct TMDL studies in order to set pollutant reduction goals needed to restore the impaired waters.

Among these advancements, the CWA requires states and some Native American tribes to adopt specific water quality standards for all water bodies in their jurisdiction. If a particular body of water violates those standards, it’s considered polluted, and a US EPA-approved clean-up plan must be created.

Setting the standards

Minnesota adopted its first statewide water quality standards in 1967, and today’s standards meet or exceed federal CWA guidelines. These standards define how much of any particular pollutant can be allowed in surface and ground waters.

These standards apply to a wide range of pollutants, including bacteria, chemicals, nutrients, turbidity and mercury.

However, the standard for any particular lake or stream depends on the designated “beneficial uses” of that water body. Beneficial uses include drinking water, supporting aquatic life, recreation, and agricultural irrigation, along with several others. Waters designated for drinking water or aquatic life often have different standards for pollutants than waters designated for recreation, agriculture or other uses. For more information on Minnesota’s standards, visit the Water Quality Standards page at the Minnesota Pollution Control Agency’s web site.

Assessing our waters

The MPCA collects water quality data from state, local and federal agencies, as well as citizen monitors, and then uses this and other information to assess waters for compliance with Minnesota’s water quality standards.

So far, we’ve only assessed a small portion of our state’s waters. However, of those waters assessed, about 40% have been determined to exceed the standards for at least one pollutant.

Adding waters to the 303(d) Impaired Waters List

If a water body fails to meet one or more of its water quality standards, that water body is considered impaired and is added to Minnesota’s Impaired Waters List. This list is also referred to as the “303(d) list” — which is the section of the Clean Water Act that mandates this assessment and clean up process.

Once a water body is listed as impaired for a certain pollutant, the Clean Water Act requires states to create clean up plan. The main tool for completing this is a process called the “Total Maximum Daily Load,” or TMDL.

Cleaning up impaired waters: The TMDL

TMDL defined

Total Maximum Daily Load (Number):
The maximum amount of a pollutant that a water body can receive and still meet water quality standards.
Total Maximum Daily Load (Study):
A written plan and analysis of an impaired water body established to ensure that the water quality standards will be attained and maintained through assigned pollution reductions.

For each impairment on the 303(d) list, the Clean Water Act requires completion of a TMDL. A TMDL is basically a pollution reduction plan for the impaired water.

The term “TMDL” actually has two complementary meanings. In numerical form, it represents total amount of a pollutant that a water body can receive and still meet water quality standards.

The TMDL also represents an extensive study of all the sources of a given pollutant contaminating the impaired water, and the amounts by which each of these contributing sources must be reduced in order to meet the standards.

The TMDL eventually results in a comprehensive pollution reduction plan. These plans don’t define how the necessary reductions will be made, but instead details how much contributing sources will be reduced in order to meet the standards. TMDLs are made available for public comment before being submitted to the US EPA for final approval.

Once a TMDL is approved, a detailed implementation plan is created to determine how each contributing source of the pollutant will achieve its required reductions. If the impairment is severe, achieving these reductions often includes extensive restoration activity and can require a substantial investment of time and resources.

Impaired waters in Minnesota

[Graph: 2008 Draft TMDLs by pollutant]

2008 Draft TMDLs by pollutant

The Minnesota Pollution Control Agency recently announced its draft 2008 Impaired Waters List. This list, updated every two years in accordance with section 303(d) the Federal Clean Water Act, indicates surface waters in Minnesota that have failed to meet water quality standards for their designated use.

The Minnesota 2008 draft Impaired Waters List shows 1,496 impairments on 336 different rivers and 500 different lakes. The year’s list includes the addition of 287 new listings. Of these new listings, 131 are on lakes and 156 are on stream or river segments. The bulk of all impairments are due to high total phosphorus, turbidity (cloudiness) and high levels of mercury in fish tissue samples. (see adjacent chart)

Once waters are listed, the MPCA is responsible for creating the clean up study portion of the TMDL. Once a water body has an approved TMDL, it is removed from the Impaired Waters List.

Minnesota’s 2006 list showed 2,250 impairments on 284 rivers and 1,013 lakes. The main reason for the decrease in total numbers in 2008 is the approved Mercury TMDL.

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.

Find out more

Minnesota Pollution Control Agency Contacts

  • For questions regarding the 303(d) list of impaired waters, contact Howard Markus at 651-296-7295 or 800-657-3864.
  • For TMDL planning or questions in general about the TMDL program, contact Jeff Risberg at 651-296-7231 or 800-657-3864.

On the Web

More data from the Impaired Waters List

Impaired waters & TMDL progress in Minnesota
TotalNew in 20082006 Total
2008 Draft 303(d) List 1,496 287 2,250
Lakes 547 131 1,088
River/Stream reaches 922 156 1,162
Conventional 989 252 781
Exotic chemicals 480 35 1.469
% Exotic chemicals 33% 65%

2008 draft TMDLs by pollutant
PollutantTotal impairments% of total impairments
Total phosphorus 315 21%
Turbidity 288 20%
Mercury in fish tissue 274 19%
Fecal coliform bacteria 147 10%
PCBs in fish tissue 134 9%
Fish bioassessment 105 7%
Low dissolved oxygen 63 4%
Macroinvertebrate bioassessment 43 3%
PFOS in water or fish 28 2%
Mercury in water 23 2%
All others 76 4%