News

Jun 28, 2025

Large portion of central Iowa water pollution tied to farming: Report

A study Polk County officials commissioned shows that Iowa's rivers, lakes and streams are plagued with pollutants that include nationally high nitrate levels, farm chemicals and harmful bacteria. The

A study Polk County officials commissioned shows that Iowa's rivers, lakes and streams are plagued with pollutants that include nationally high nitrate levels, farm chemicals and harmful bacteria.

The draft report, originally expected to be delivered in March, comes as Central Iowa Water Works issued its first-ever lawn watering ban for its 600,000 customers two weeks ago. The regional authority said high nitrate levels in the Raccoon and Des Moines rivers made it difficult to treat enough water to meet rising demand from lawn watering.

At the same time utilities are struggling with high nitrate levels, Des Moines area business, government and civic leaders propose investing $120 million to make the rivers more attractive for recreation, including new river trails and a downtown wave-making machine that supports surfing.

In 2023, Polk County supervisors commissioned a comprehensive study of the Des Moines and Raccoon watersheds, spending $1 million in federal American Rescue Plan money to pay for the work. Sixteen water scientists worked over 4,000 hours to produce the five-page summary, a 108-page overview and a longer technical document.

Iowa Capital Dispatch released a draft of the overview Thursday, June 26. Also Thursday, the Des Moines Register obtained drafts of the summary and the technical document.

Polk County "faces many threats to its waters," including human activities in the Des Moines metro's urban areas and the upstream rural landscape. The assessment found that agriculture contributes about 80% of all nitrogen in the Des Moines River and the Raccoon River.

Polk County supervisor chair Matt McCoy said the county hopes the findings "will lead to further investments in improving our watersheds, which will ultimately have positive impacts on public health, recreation and economic benefits."

Meanwhile, while the lawn watering ban continues, heavy rains are bringing down nitrate levels in the Raccoon and Des Moines rivers, central Iowa’s primary drinking water sources, easing concerns that the regional water authority may require greater water restrictions.

The water remains safe for residents to drink, said Tami Madsen, Central Iowa Water Works executive director, on Thursday, June 26. She avoided commenting directly on the report's findings, saying the regional authority will continue working with state farm groups on water quality.

Polk County is expected to release the final report Tuesday, July 1. Here's what to know about the draft and its delay:

Polk County spokesperson Jon Cahill said in a statement the county needed time to review it and build a public information campaign for the study's rollout, including a video and news releases.

"Polk County reserves the right to release the report when we are ready," Cahill wrote. "Our internal analysis began when we received the report six weeks ago. Knowing it would take some time for our internal due-diligence Polk County set the date of July 1 for the release of the full report to the public at our regularly scheduled public meeting."

The Register requested a copy of the report June 5. That public records request is still pending.

The draft report says the Des Moines and Raccoon rivers “often contain some of the highest nitrate levels in the U.S. and routinely exceed the health-based drinking water standard, threatening human health and increasing the cost and complexity of water treatment” for central Iowa utilities.

“Emerging research suggests ingesting levels of nitrate even below the current drinking water standard can pose health risks, increasing the urgency for addressing the issue today,” the summary says.

Federal drinking water regulations limit nitrate levels in drinking water to 10 milligrams per liter. Levels above that make the water unsafe for pregnant women and infants under 6 months. Consuming water with high levels of nitrates is associated with infant asphyxia, known as blue baby syndrome, and even lower levels of nitrates have been linked to cancer and birth defects.

Nitrates occur naturally in soil, but in heavily agricultural states like Iowa, they also leach from manure and commercial fertilizer applied to farmland into rivers, lakes and streams, often via drainage tiles underlying fields. Fertilizers also can wash into waterways from urban sources like lawns and golf courses.

Both pressures of poor source-water quality and heightened demand challenge central Iowa’s drinking water security, according to the study’s summary.

The nitrate levels in central Iowa are among the highest in the nation and routinely exceed the health-based drinking water standard, which threatens human health and increases the cost and complexity to treat the water, the study said.

Reducing the nitrate levels in the rivers will require a “watershed-scale” approach that goes beyond the current strategy. This includes “regenerative agricultural production and appropriate oversight and management of upstream manure disposal,” the study states.

Long-term monitoring found over half of the field samples from the Raccoon River at Fleur Drive exceeded the EPA’s swimming advisory threshold for E. coli, and about 15% surpassed the higher level for activities that require less contact with river water, like wading and boating, the study found.

The analysis considers multiple pollutants, but emphasizes four agriculture-linked stressors: nitrate, phosphorus, fecal bacteria and microbe-generated toxins.

Iowa Agriculture Secretary Mike Naig didn’t respond to a request for comment. But his office provided a LinkedIn post, calling high nitrate levels for central Iowa utilities a “serious situation,” adding that “it’s not uncommon to observe nutrient spikes during a wet spring.

“There are several contributing factors — non-point source, water treatment capacity and weather — and addressing the issue requires a multi-pronged approach. Agriculture, conservation, recreation, and urban and business growth can co-exist in Iowa,” Naig said on LinkedIn.

"Managing inputs is important, but we also need conservation practices, like cover crops, wetlands and saturated buffers, to minimize soil erosion and filter nitrates from the runoff," Naig wrote. "Cities can also play a role and install urban conservation practices to manage stormwater and prevent sediment runoff from paved and residential areas."

Iowa Farm Bureau Federation said it hadn’t seen the report and couldn’t comment.

The draft "confirms that central Iowa’s waterways are significantly impacted by agricultural pollution, particularly nitrates and fecal bacteria, which pose serious risks to public health," said the Iowa Environmental Council.

"This report highlights the need to change our approach to water quality," the Des Moines-based group said in an email, adding that voluntary conservation practices "are not sufficiently protecting our source water supplies, and the recent nitrate levels in the Raccoon and Des Moines Rivers continue to provide evidence.

"Just as the report mentions, comprehensive watershed planning, clear benchmarks for progress, funding for additional water monitoring, and improved manure management will be keys to safeguarding public and environmental health," the group said.

The study also proposes multiple actions on the state, county and utilities level, including:

Donnelle Eller covers agriculture, the environment and energy for the Register. Reach her at [email protected].

Nick El Hajj is a reporter at the Register. Reach him at [email protected].

Virginia Barreda is the Des Moines city government and Polk County reporter for the Register. She can be reached at [email protected]. Follow her on X at @vbarreda2.