Prairie Rose Lake included on DNR’s impaired waters list

HARLAN —Prairie Rose Lake in Shelby County has once again been listed as impaired in the 2026 Integrated Report released by the Iowa Department of Natural Resources. 
The impaired waters list evaluates retroactive monitoring data to determine whether a water segment meets established criteria for its designated uses. When a waterbody is classified as impaired, it enters a restoration process under the federal Clean Water Act.
The Iowa DNR has been treating Prairie Rose Lake with aluminum sulfate (alum) to bind phosphorus and reduce algae blooms. While these treatments have improved water clarity, the lake remains on the list.
According to the DNR’s assessment database, the lake continues to fail water-quality standards due to long-standing issues with excessive algae growth and turbidity, along with elevated E. coli bacteria levels at the swimming beach. Lake assessments are based on monitoring data collected between 2020 and 2024.
Statewide, the draft biennial report identifies more than 700 rivers, lakes and wetlands that do not meet designated uses such as recreation, fishing or drinking water. 
Other Western Iowa waters included on the impaired list include the Boyer River, Carter Lake, East Nishnabotna River, East Nodaway River, Lake Manawa and Middle Nodaway River.
The 2026 draft uses water-quality data from 2022 to 2024 for rivers and streams and 2020 to 2024 for lakes. Compared to the 2024 report, the new draft lists three fewer impaired segments. In a news release, the DNR said the total number of impaired waters has remained “relatively stable” from 2014 through 2024.
The report does not include seven nitrate-impaired segments the U.S. Environmental Protection Agency attempted to add in late 2024. The DNR challenged those additions, and the EPA later removed them.
However, the 2026 draft does list two nitrate-impaired river segments,  one on the Iowa River and one on the Raccoon River. The DNR said it did not change its nitrate assessment criteria from 2024 to 2026, but updated monitoring data warranted the new listings.
The draft impaired waters list is open for public comment for 30 days before it is submitted to the EPA. Comments may be submitted by email to IRcomment@dnr.iowa.gov through March 19, 2026.