Iowa's Impaired Waters List: Revisions & Interventions

DNR Proposal and Response from the EPA 

Iowa's Impaired Waters List identifies the lakes, wetlands, streams that do not meet water quality standards for point source and non-point source pollutants. Section 303(d)(2) of the Clean Water Act requires all states to develop an Impaired Waters List every two years, and the Environmental Protection Agency (EPA) enforces that requirement. The Iowa Department of Natural Resources (DNR) submitted the proposed 2024 list to EPA in May.  

The DNR analyzed 1,428 waterbody segments for the state’s Impaired Waters List. At the time of submission, the report showed a net reduction of 84 impaired segments from the 2022 report. EPA evaluated the state’s submission and determined in November that it was not fully consistent with the requirements of the Clean Water Act. 

These discrepancies and delisted segments are a result of methodological differences between the EPA and DNR for evaluating Iowa’s waterbodies. Namely, the EPA stated that the DNR did not utilize publicly available data from the Iowa Water Quality Information System, and the reliability of the data reflected in the Impaired Waters List. The EPA found “there are questions and uncertainty about whether the available data and information are temporally or spatially representative or adequately reviewed for quality control. In some instances, samples were collected as single samples or multiple samples collected within a single day, which are the only existing and readily available data and information for the location.” 

During its review, EPA identified seven impairments on six river segments that should have been included on Iowa’s Impaired Waters List, including one segment on the Cedar River, two segments on the Des Moines River, two impairments on one segment on the Iowa River, one segment on the Raccoon River, and one segment on the South Skunk River. The EPA disapproved of the state’s decision to not list these segments as available data and public information indicate they have compromised water quality.  

EPA determined that these areas exceed the nitrate drinking water standard of 10 milligrams per liter (mg/L). EPA disagreed with DNR’s method of determining how often the water could exceed the drinking water standard, which the DNR has used for years. Excess nitrate in drinking water can pose devastating consequences for human health. Hundreds of thousands of Iowans rely on the seven impaired waterways that are not included in the DNR’s provided Impaired Waters List for drinking water. Regardless of the quality in the rivers, drinking water utilities must meet drinking water standards. 

Although not included in the Impaired Waters List, the DNR maintains a record of Waters in Need of Further Investigation (WINOFI) and Category 4 impaired waters, which includes waterbodies that are impaired, but a Water Quality Improvement Plan (also known as a Total Maximum Daily Load – TMDL) is not required. These distinctions are important as they can skew Iowa’s water quality away from scrutiny while potentially degrading water quality. Segments from the Cedar River, Des Moines River, Iowa River, and South Skunk River are on the WINOFI list and also part of the EPA’s added waterbodies. 

Interventions to Monitor and Improve Water Quality 

EPA and DNR have disagreed about the best way to assess monitoring data for drinking water uses, but the threshold of 10 mg/L is clear. There are ways that the DNR can better evaluate water quality in other water bodies where Iowa lacks such a bright line. Current rules prohibit “aesthetically objectionable conditions” for other uses of state waters, which is not as easy to measure. Setting numeric nutrient criteria (NNC) would establish nitrogen and phosphorus limits for specific water bodies. This data-based method would make it possible to measure how each water body compares to the standard. 

IEC and other groups have been calling for the DNR to adopt NNC, particularly in Iowa’s recreational lakes, for years. IEC and the Environmental Law & Policy Center have twice petitioned the Environmental Protection Commission (EPC), a citizen board that oversees DNR, to direct DNR to begin developing NNC . The EPC denied both petitions based on the DNR’s argument that the Iowa Nutrient Reduction Strategy exists and should be given more time to work. However, IEC’s assessment, as well as other research, has demonstrated that the Nutrient Reduction Strategy has not been effective and more thorough action is needed. 

The EPA recommends methods for states to develop state-specific numeric nutrient criteria to closely monitor water quality and limit errors in Impaired Waters Lists. The EPA even used actual water quality data from Iowa as a case study (see page 98) to show how to apply the methods here. The results of the case study provide a scientific basis for Iowa to adopt NNC. 

Ways to Get Involved 

EPA is opening a 30-day public comment period, recently extended to December 19, to receive comments concerning the decision to add the seven impairments to Iowa’s 2024 Impaired Waters List. Written comments must be sent by email to R7-WaterDivision@epa.gov on or before December 19, 2024.

View IEC's comments on our Public Comments page.