The Iowa Department of Natural Resources has issued its every-other-year impaired waters report showing only a slight 2 percent increase in the number of impaired waters, the smallest increase seen in recent reporting cycles, the DNR says. And yet, every two years the release of the list seems to cause frustration among farmers and the public. So what good does it do?

First, I want to be clear about one thing: Iowa farmers are taking on the challenge of improving water quality. There's overwhelming data to support this fact, including:

  • The value of the long-term investment by farmers and the public is estimated at $6.2 billion, according to a 2018 statewide LiDAR mapping of just six types of conservation practices (terraces, ponds, grassed waterways, water and sediment control basins, contour strip cropping and contour buffer strips/prairie strips).
  • An Iowa State University survey showing the majority of farmers report increased use of soil testing, precision farming practices, decreases in fall nitrogen applications and more in-season applications, and increases in construction of conservation structures like terraces, grassed waterways and sediment control basis.
  • A more than 20-fold increase in the acres planted to cover crops, a 6-fold gain in restored wetlands, and a 4.5-fold gain in acres protected by cost-shared terraces in recent years. 

Despite clear trends of these and other conservation gains over the long-term, there was still a small increase in the number of impaired waters in the DNR report. However, it does not mean that water quality is getting worse, according to the DNR. This report is not designed to gauge changing water quality trends or the magnitude of impairments or improvements, or the extent to which a stream or lake does not meet state water quality standards established for their intended beneficial uses, such as swimming, fishing or drinking water. Water quality officials and state and federal natural resource agencies look at other available data and conduct other analysis for those needs. Those reports can be detailed, complex and often conflicting.

This latest biannual impaired waters report is a snapshot of where the state is relative to monitored streams and lakes meeting the water quality standards to protect their beneficial uses. The factors affecting that threshold can include variable weather, stricter standards and more intense monitoring. It's not always due to human activity, but sometimes is.

In addition, the degree of impairment ranges but is generally slight to moderate. The vast majority of waters are safe for use. Even waters considered high-quality such as Deer Creek in Mitchell County, the Volga River in Fayette County and West Okoboji Lake in Dickinson County can still have some degree of impairment. And even if one segment is impaired, that does not mean the entire stream or river is impaired.

How is the Impaired Waters List Generated?

The state first does an overall assessment report of all monitored waters, required by Section 305(b) of the federal Clean Water Act. You can find that overall water quality assessment database on the DNR webpage at this link. From this database, the DNR then prepares the biannual listing of waters in need of more monitoring, that are meeting water quality criteria, or that are impaired or not meeting their water quality standards. For each impaired water on the list, the state identifies the pollutant causing the impairment, when known, and then assigns a priority for development of a Total Maximum Daily Load (TMDL) or watershed improvement plan, based on the severity of the pollution and the sensitivity of the water's designated beneficial use and other factors.

The impaired waters report lists the waters and the number of impairments caused by pollutants (such as chemical compounds) and pollution (caused by human activity) including: bacteria, biological impacts, fish kills, mercury, low dissolved oxygen, pH, habitat and hydrology impacts, ammonia, temperature and nitrate (for drinking water uses).

In recent years, these two steps or reports, have been combined and are sometimes called the "integrated report" of all monitored and impaired waters. This integrated report contains five sections or categories. The most attention is focused on one category: Category 5, the impaired waters listing or water segments requiring a TMDL.

What is a TMDL?

Under Section 303(d) of the Clean Water Act, states are required to evaluate all available water quality-related data and information to develop a list of waters that do and do not meet water quality standards, or might not meet them sometime in the next two years before the next report (considered a "threatened" water). There are others categories within the list that report-out other findings, too, such as all designated uses are met, some of the designated uses are met but there's insufficient information to determine whether the remaining uses are met, there's Insufficient information to determine whether any uses are met, and the waterbody is impaired but a TMDL is not required.

For those water segments where enough data exists to call it impaired, states must develop a TMDL for every pollutant/waterbody combination on the impaired waters portion of the list. An essential component of a TMDL is the calculation of the maximum amount of a pollutant that the waterbody can receive and still meet water quality standards. Standards can be numeric thresholds or general, descriptive "narrative" standards (also known as the "free froms," that is, free from certain negative conditions or "aesthetically objectionable conditions" such as excessive algae).

The Clean Water Act requires states to allocate the TMDL loading capacity for a given stream, lake or wetland among the various point sources (cities, industries) and non-point sources (agriculture). Permits for point sources (e.g., municipal waste treatment plants and large industries) are issued through the EPA’s National Pollutant Discharge Elimination System, or NPDES program. Section 319 of the Clean Water Act provides for federal grants to support technical and financial assistance, education, training, technology transfer, demonstration projects and monitoring to support the nonpoint source portion of an impairment.

How is the Impaired Waters List Used?

In addition to point source permitting, the DNR and other state and federal natural resources agencies and local organizations use the impaired waters list to target very limited nonpoint source financial and technical support to cooperative programs and projects that address the impairments. Demand for these cost-share programs always exceeds funds available. 

For example, county soil and water conservation districts and their partners use the list to apply for targeted federal and state cost-share funding for specific watersheds and farms to reduce sediment or nutrient loading that may come primarily during large rain events. But the list and the watershed projects that may result also give confidence to the agencies and to the farmers independently considering the same recommended practices and structures in the TMDL watershed improvement plan that they often fund and build on their own.

These details are certainly confusing aspects to most Iowans. It is often misinterpreted by the media and the public. The DNR has been working to improve knowledge about and use of the report. Improvements can still be made in the report. It can be a useful planning tool for state and federal conservation agencies and their local partners. It can help Iowans achieve more conservation progress.

However, it is not an assessment of overall water quality trends or success of other strategic plans, such as the Iowa Nutrient Reduction Strategy or its implementing Water Quality Initiative, and should not be used for those purposes. Those initiatives are relatively new. Science and experience shows it will take many years of sustained effort for success at a statewide scale. Progress will continue to be measured by additional new watershed projects, additional practice implementation, and sustained funding over time.

Report Details

In the DNR impaired waters report, of the 1,421 water segments assessed:

  • 363 fully met the Iowa water quality standards for their intended use
  • 523 were identified as waters in need of further investigation
  • 145 were considered impaired but a TMDL was already completed or is not needed
  • 622 did not fully meet the standards needed for their intended use and were place don the "impaired Waters list" and will be prioritized for a TMDL
  • 1,142 segments and 1,040 beneficial uses were not assessed
  • 17 water segments and 27 previously impaired beneficial uses are proposed by DNR to be removed form the 2016 list due to new data, errors found or documented water quality improvements (Note: 56 previously impaired beneficial uses were removed from the 2016 list in the last reporting cycle.)

More information about the draft Iowa impaired waters list can be found at this DNR link, including an interactive map of all draft 2018 impaired water segments. A DNR summary news release can be found here.

Public comments on the draft list will be taken through December 28. Email comments to Dan Kendall at:, or send them to: Iowa Department of Natural Resources, Attention: Dan Kendall, Water Quality Monitoring & Assessment Section, Wallace State Office Building, 502 East 9th Street, Des Moines, IA 50319.