The Iowa Department of Natural Resources released a draft version of its 2026 biennial integrated report Tuesday, which listed more than 700 segments of rivers, lakes or wetlands in the state as impaired.
The impaired list looks at retroactive data and determines if a water segment meets, or fails to meet, designated criteria for uses like fishing, recreation or drinking water. Once a segment is listed as impaired, it triggers a restoration process under the federal Clean Water Act.
The recent draft of the list, which is open to public comment for 30 days before it will be sent to the U.S. Environmental Protection Agency, comprises water quality data from 2022-2024 for rivers and streams and data from 2020-2024 for lakes.
With each report, segments move off the impaired list or are “delisted” and other segments are added to the list. The 2026 draft report has three fewer segments listed than the report did in 2024.
In a news release about the draft, DNR said the number of impaired segments have been “relatively stable” from 2014 to 2024.
These figures do not include, however, the seven segments that EPA attempted to add to the list in late 2024 due to nitrate impairment. DNR challenged EPA’s additions to the list and the segments were removed by EPA over the summer.
The 2026 draft lists two segments of river, one on the Iowa River and one on the Raccoon River that are impaired for nitrate. DNR said it did not change its criteria from 2024 to 2026 for assessing nitrates, but the data analyzed for the newest list warranted the impairment listing.
The DNR assessed more than 213,000 data points and sorted water segments into five categories. Waters put in either category four or five are considered impaired and may or may not need a “pollution budget” or a Total Maximum Daily Load plan that allows the department to set safety standards, discharge permits and restoration efforts to help bring impairment into acceptable ranges.
A category four designation means the water fails to meet some of its designated uses, but it does not need a TMDL. Category five water segments do require a TMDL and comprise the Section 303(d) list of impaired waters that is submitted to the EPA.
A section of the Iowa River north of Iowa City was listed as impaired on the 303(d) list, or as a category 5 impairment, because “significantly” more than 10 percent of samples failed to meet allowable criteria for nitrogen.
DNR said that while the impairment and TMDL would be issued for nitrogen, it would address “all species in the nitrogen cycle, including nitrates.”
A segment of the Raccoon River, as it flows through West Des Moines and into the Des Moines River, had a category 4 impairment for nitrate concentrations above allowable criteria in significantly more than 10 percent of samples. DNR records show that the same segment has had a category 4 impairment designation since 2016, for either E. coli or nitrate.
The latest report had 574 category 5 impaired segments and 149 category 4 impaired segments, for a total of 723 impaired sections of river, lakes or wetlands.
The report shows DNR assessed more than 1,100 river segments, of which about 51 percent were designated impaired. Twenty-six percent of the streams supported their designated uses and 23 percent of segments were in need of further investigation.
Of the 565 total impaired stream segments, nearly 450 were impaired due to the presence of indicator bacteria and more than 150 were impaired due to biological reasons, which means an assessment found fish or other aquatic life populations are not present in the amounts expected for the segment.
Lawmakers have introduced a bill this year that would require DNR to determine the animal source of indicator bacteria before it could list a water segment as impaired. DNR staff, however, have said they don’t currently have the technology to determine the percentage of fecal bacteria coming from each animal species that contributed to the impairment.
DNR Water Quality Monitoring & Assessment Supervisor Mark Moeller spoke to the Iowa Environmental Protection Commission Tuesday and said an impairment designation does not necessarily mean a water segment is highly polluted or unsafe.
“You can have all these parameters that are analyzed, if only one parameter is not meeting the standard, then it’s impaired,” Moeller said.
While a river might be impaired for fish consumption, it could still be safe for swimming and kayaking or as a drinking water source.
And, while some segments have been on the impaired list for decades, Moeller said the process is “cyclic” as new data enters the mix every two years.
“It’s a prioritization tool for the Clean Water Act, it’s not necessarily a signal of very polluted conditions,” Moeller said.
The draft will be open to public comment for 30 days. Comments on the draft can be submitted to IRcomment@dnr.iowa.gov by March 19.
Cami Koons covers agriculture and the environment for Iowa Capital Dispatch, where this story first appeared.
