A coalition of environmental advocacy groups has filed a federal lawsuit against the United States Environmental Protection Agency (EPA), challenging the agency's decision to rescind impairment listings for seven major river segments in Iowa. The complaint underscores an intensifying debate over agricultural runoff and regulatory oversight as Iowa grapples with water quality issues, demonstrated recently by Des Moines Water Works’ second-ever watering ban on June 8 and the passage of HF 2771, a bill injecting around $320 million into long-term watershed conservation, water monitoring, and municipal filtration infrastructure upgrades. By targeting the EPA's reversal, the lawsuit seeks to reinstate impaired status designations for waterways impacted by high nitrate and nitrite levels.
Under Section 303(d) of the Clean Water Act (CWA), states are required to submit a list of “impaired waters”—water bodies that fail to meet certain water quality standards—to the EPA every two years.[i] The complaint, filed on May 14 by advocacy groups Food & Water Watch, Iowa Environmental Council, and the Environmental Law & Policy Center, concerns the proposed impaired waters list the Iowa Department of Natural Resources (DNR) originally submitted to the EPA in 2024. In assessing nitrate and nitrite levels for state waters, the DNR applied a method of binomial analysis[ii] developed by the EPA for what the federal agency categorizes as “conventional pollutants.” This methodology classifies waters as impaired where pollutant levels in waterways exceed safe drinking water standards more than 10% of the time.
The EPA initially rejected this approach, reasoning that the “10% rule” should not be used for nitrate and nitrite because of their known toxicity. As a result, in December 2024 the EPA issued a partial disapproval and formally designated seven additional river segments—spanning the Cedar, Des Moines, Iowa, Raccoon, and South Skunk Rivers—as impaired. This mandatory listing triggers a requirement under the CWA to develop strict pollutant standards referred to as Total Maximum Daily Loads (TMDLs), effectively placing these rivers on a water quality restoration plan.
The EPA’s partial disapproval was reversed in July 2025. EPA Region 7 Administrator James Macy sent a two-page letter to the DNR on July 11 rescinding the federal impairment listings, explaining that the EPA needed to reevaluate its decision in light of (1) additional information from the DNR “not previously submitted to or considered by the EPA”; and (2) an error made in the EPA’s initial decision to partially disapprove the DNR’s list by considering criteria for nitrate and nitrite standards “applicable to both chronic and acute human health effects” rather than solely chronic effects.
The plaintiffs' complaint challenges the EPA's reversal through two claims:
- Arbitrary and Capricious Action under the Administrative Procedure Act (APA).
The APA prohibits agency action that is “arbitrary, capricious, an abuse of discretion, or otherwise not in accordance with law.”[iii] The plaintiffs assert that the EPA's rescission in this case was arbitrary and capricious because the agency received no genuinely new information as a basis for its reversal. They characterize the documents provided by the DNR after the partial disapproval as “only includ[ing] items previously sent to the EPA for approval” in 2001 and 2002, along with the EPA’s own response to these documents. The plaintiffs further argue that the EPA used the correct nitrate and nitrite standards under Iowa law in its initial disapproval, noting that Iowa's water quality standards (1) independently mandate that toxic or detrimental substances be limited to safe concentrations; and (2) expressly mirror federal Maximum Contaminant Levels (MCLs), which apply to all drinking water samples to protect public health from both acute and chronic harm.
- Failure to Perform a Nondiscretionary Duty under the Clean Water Act.
Alternatively, if the rescission letter is not viewed as a final agency action, the plaintiffs claim that the EPA has violated the Clean Water Act's deadline to issue a final approval or disapproval of Iowa's impaired waters list. In disapproving a state’s impairment listing, a Regional Administrator “shall, not later than 30 days after the date of such disapproval, identify such waters in such State and establish such loads for such waters as determined necessary to implement applicable [Water Quality Standards].”[iv] The complaint argues that the EPA failed to meet this standard because the agency has taken no further action since Administrator Macy’s letter was issued on July 11, 2025.
The EPA has not yet submitted a response to the complaint. CALT is monitoring this case’s docket and will provide updates as it progresses.
[i] 33 U.S.C. § 1313(d)
[ii] A binomial analysis is a statistical test where a series of numeric inputs are sorted into two categories (typically “pass” and “fail”) and a mathematical formula determines the probability of a specific number of successes or failures occurring within a given number of total samples. Here, samples are sorted into either passing or failing the safe drinking water standard. While the target threshold for conventional pollutants in this case is an exceedance rate of no more than 10%, a binomial analysis uses sample size and probability to determine with a high degree of statistical confidence that a river segment actually exceeds that 10% threshold before an agency categorizes it as impaired.
[iii] 5 U.S.C. § 706(2)(A)
[iv] 40 C.F.R § 130.7(d)(2)