Nitrate levels in Iowa water remained high through fall, data show

Nitrate concentrations, exacerbated by a wet spring that followed years of dry conditions, reached near record highs in Iowa rivers this summer.

Concentrations are typically elevated in the summer. The past several years, nitrates have dropped to near-zero concentrations in late summer through early winter. But this year, concentrations in rivers and in central Iowa’s drinking water have remained high.

Water quality advocates say the 2025 trend is further evidence that the state should prioritize long-term funding for water quality monitoring. Monitoring that included a longer timeline, they say, would show if these trends were consistent with similar weather patterns in the past, or indicative of what many have called a water quality crisis in the state.

  Buy Photo

Larry Weber, the director of hydroscience and engineering in the College of Engineering at the University of Iowa, said regardless of where this year stacks up compared to previous years, it’s clear that nitrate concentrations have increased in Iowa over the past decades.

“Not only should we have the sensors we have, we should have more out there to provide a more uniform network across the entire state,” Weber said.

Des Moines Water Works collects and publishes data on samples of its finished water, or water that has been treated at the facilities, and of its source waters, including the Raccoon and Des Moines rivers.

This summer, Iowa Capital Dispatch compared nitrate concentrations in 2024 and 2025 using data from Des Moines Water Works.

Melissa Walker, communications and outreach manager for Des Moines Water Works said in a statement that it is “not unprecedented” for levels to increase in the fall. This is usually due to fall fertilizer application and precipitation.

Walker said the Raccoon River also had high levels of nitrate concentration in November and December of 2014 and 2015, when the state experienced a “similar weather pattern of a multi-year drought period followed by a wet fall.”

Nitrate concentrations in central Iowa over the summer were similar to levels recorded in 2013, though this year marked the first time that Central Iowa Water Works was forced to issue a lawn watering ban to keep system demand low enough to remain within the U.S. Environmental Protection Agency safe drinking water limits for nitrate.

The EPA holds that nitrate concentrations below 10 milligrams per liter are safe to drink. This limit was set to mitigate the risk of blue baby syndrome, which can be fatal to infants.

Des Moines Water Works has a nitrate removal system that runs when levels in source water, the Des Moines and Raccoon rivers, are too high.

Walker said while levels are “higher than average” this fall and heading into winter, it has not been high enough to require use of the nitrate removal system at the plants.

The system ran for 122 days in 2025 and shut off in August, according to Walker. She said levels have been low enough in the Des Moines River and the infiltration gallery, a series of underground pipes that collects alluvial ground water through more than three miles in Water Works Park, to continue making water within EPA limits.

Des Moines Water Works has recently called for efforts to reduce upstream pollution. It opposed a recent EPA decision to not label segments of the source water rivers as impaired due to their nitrate concentrations.

Colleen Fowle, the water program manager with the Iowa Environmental Council, said the elevated levels this fall “highlight that the problem isn’t going away.”

Fowle said many Iowans only think of the nitrate issue during something like the lawn watering ban, or during the early flushes of summer when concentrations are highest.

“But public water suppliers don’t have that luxury, and they are thinking about these levels every single day, because they’re tasked with delivering safe water to us,” Fowle said.

While Des Moines Water Works offers easily accessible data, the Des Moines and Raccoon rivers are not the only rivers through Iowa that have had elevated nitrate concentrations through fall.

Data from the Iowa Water Quality Information System, or IWQIS, show other major rivers also have been elevated above past years.

Most of the sensors show data back to 2021, though some are newer and don’t show data beyond 2025.

A sensor on the Cedar River in Palo shows 2025 levels in the river were higher this fall than in the previously monitored years, aside from small spikes.

The differences in the Cedar River and also in the Iowa River, at a sensor in Iowa City, are less drastic than those observed in Des Moines along the Raccoon and Des Moines rivers, but still show elevated levels through fall 2025.

Weber said precipitation along with livestock operations, manure and fertilizer applications to fields are the “key factors” in the trend of higher nitrate concentrations.

“This long-term, continually evolving trend towards higher levels … this is just the status and trend of where the state is going,” Weber said.

While this fall was fairly dry, he said it wasn’t quite as dry as the previous couple of falls, which likely had lower nitrate levels because of abnormal dryness.

In addition to river monitoring, IWQIS has sensors on several tiles, or underground pipes connected to agricultural land, that outlet to streams. According to the data in the system, these tile lines have consistently high – between 10 and 30 mg/L – concentrations of nitrate throughout most of the year. Unlike the river data, these concentrations are not noticeably higher in 2025 than other recorded years.

Weber said when comparing 2025 to the data in the system, which goes back only to 2021, 2025 looks like the outlier. But really, he said, 2025 is closer to “normal hydrologic conditions” for Iowa.

“This year in many parts of the state, we’ve had some persistent rains that have kept those tiles flowing, and when the tiles are flowing, the nitrate concentrations are high,” Weber said.

Tiles help to drain excess water, often along with nutrients applied to and naturally occurring in the soil, from cropland. When the soil is moist, the tiles flow. When the soil is dry, the tile isn’t shipping those soil nutrients downstream.

Archival data from the U.S. Drought Monitor shows more severe drought conditions across the state in the fall months of 2021, 2022, 2023 and 2024 than what Iowa experienced this fall.

Weber said the conversation around nitrate concentrations is consistently about comparing this year to last year, or this month to that month, but he said that’s where the “argument gets lost.”

“What we can convincingly say is that if we go back 75 years ago, it was one milligram per liter,” Weber said of nitrate concentrations in Iowa rivers. “Fifty years ago, it was two to three milligrams per liter and now we’re consistently in the six to eight milligrams per liter — with many times above 15 to 20 — and that’s simply high compared to where we were 50 years ago.”

Farm groups say water quality is improving

An increase in nitrate concentration over this time period in Iowa rivers is shown in a recent Polk County-commissioned study, the Central Iowa Source Water Resource Assessment, which pointed to agriculture as the No. 1 contributor.

A recent opinion column signed by farm commodity groups and published by Iowa Farm Bureau disputed claims made about the report and instead argued that Iowa Nutrient Reduction Strategy data show Iowa water quality is improving.

The strategy’s collected data on nitrate load, divided by streamflow each year, show that since the early 2000s, when the monitoring began, the five-year average nitrate load in Iowa rivers has decreased.

The nutrient strategy collects data to show the impact that conservation strategies, like cover crop adoption, buffer strips and reduced tillage, have on the nutrient load that eventually ends up in the Mississippi River.

The opinion article from the farm commodity groups, including Iowa Farm Bureau, Iowa Corn Growers Association, Iowa Soybean Association, Iowa Pork Producers Association, Iowa Cattlemen Association and Iowa Nutrient Research & Education Council, said “progress takes time, but it is happening.”

“Iowa farmers care deeply about the land and water they use to grow their crops,” the opinion article read. “To move forward, we must reject misleading generalizations and instead focus on proven, science-based solutions. Iowa’s water quality challenges are real, but so is the progress we’ve made and our resolve to do more.”

United call for information

According to Weber, the IWQIS sensors were placed to monitor individual practices and tile lines, the nutrient load leaving the state and to look at targeted watersheds for nitrate removal systems.

In 2023, the Legislature redirected funding from the monitoring system. It was temporarily propped up by money from the Walton Family Foundation, but is set to expire in summer 2026. Weber has been pleading with the state and local governments to support the monitoring system.

Already, Polk County has pledged $200,000 to keep the monitors running, and other populous counties are considering similar allocations.

Weber is focusing on funding the system, which needs about $600,000 annually to operate.

“I’m not asking for money for us in our program,” Weber said. “I’m asking for money for the people of Iowa, because this network is important in protecting their health and understanding the water quality concerns that we have statewide.”

Fowle with IEC, which has advocated to fund IWQIS, said it’s “unprecedented” for a coalition of nonprofits to enter an upcoming legislative session, “pretty much all in agreement” that funding the system is the “first step” to help solve the water quality “crisis” in the state.

“This isn’t going to be solved overnight, but there are some steps we can take in the short term and in the long term,” Fowle said. “First and foremost, we have to make sure we have good data, and that data is accessible to everyone in Iowa.”

This article first appeared in the Iowa Capital Dispatch.