The Iowa Department of Natural Resources has released its draft 2026 Impaired Waters Report, and it shows more than 700 segments of rivers, lakes, and wetlands across Iowa are failing to meet at least one of their designated uses.
The biennial report is required under the federal Clean Water Act and evaluates whether waterways meet standards for recreation, aquatic life, drinking water, or human health.
The DNR analyzed more than 213,000 water‑quality data points collected between 2022 and 2024 for streams, and 2020 through 2024 for lakes. Statewide, the draft lists 723 impaired segments—three fewer than the 2024 report. Officials emphasize that an impairment does not necessarily mean a waterbody is unsafe; a segment can fail one parameter while remaining suitable for other uses.
Across northwest Iowa, the report highlights four major recurring issues.
The most common is indicator bacteria, which continues to affect stretches of the North Raccoon River, the Little Sioux River, Mill Creek, Odebolt Creek, and several tributaries.
Biological impairments—meaning fish or other aquatic life are not present in expected numbers—also appear throughout the region, including on segments of the North Raccoon, Little Sioux, Waterman Creek, Lizard Creek, Battle Creek, and Prairie Creek.
In area lakes, algae and chlorophyll-a levels remain a concern at Storm Lake, Black Hawk Lake, Lost Island Lake, Five Island Lake, Twin Lakes, and Trumbull Lake.
Turbidity and clarity issues continue to affect many of those same lakes, including Storm Lake, Black Hawk Lake, Lost Island Lake, Virgin Lake, Medium Lake, and Twin Lakes.
Statewide, nearly 450 stream impairments are tied to bacteria, and more than 150 are linked to biological conditions. The DNR says identifying the exact source of bacteria remains a challenge, and while lawmakers have proposed requiring the agency to determine the animal source before listing a segment as impaired, staff say the technology to do that does not currently exist.
The draft report also includes nitrate‑related impairments on portions of the Iowa and Raccoon Rivers—marking the first nitrate listings added by the state since EPA attempted to add seven segments in 2024, additions the DNR successfully challenged.
The DNR describes the impaired waters list as a “problem‑identifying tool” that helps prioritize restoration work, not a declaration that a waterbody is unusable. Water segments can be removed from the list when new data shows improvement or when a Total Maximum Daily Load plan—a pollution budget—is completed.
The draft report is open for public comment through March 19. Comments can be submitted by email to IRcomment@dnr.iowa.gov. A link to the full report is available at iowadnr.gov.
