Central Iowa Nitrate Pollution: Synthetic Fertilizer Is the Biggest Culprit, New Data Shows

Central Iowa's drinking water is being hit hardest by synthetic fertilizer runoff, not urban pollution or corporate farms, according to a comprehensive new analysis from Polk County. The report, called 'Currents of Change,' found that synthetic fertilizer accounts for 40% of the nitrates entering the Raccoon and Des Moines rivers, the primary sources of drinking water for the Des Moines metro area.

The findings come as Iowa continues to grapple with water quality challenges, particularly after heavy rainfall followed last year's drought conditions. Nitrates, a naturally occurring form of nitrogen essential for plant growth, become problematic when large amounts wash off farmland and into waterways.

What is driving nitrate pollution in Iowa's rivers?

Researchers sorted nitrate entering the Raccoon and Des Moines rivers into six distinct sources. The breakdown shows agriculture dominates the problem, while urban sources play a surprisingly small role:

• Synthetic fertilizer (40%): Fertilizer spread on fields that crops don't absorb is the biggest nitrate source for both rivers.
• Soybean plants (20%): Soybeans pull nitrogen from the air and store it. When the plants break down after harvest, that nitrogen can wash into waterways.
• Fertilizer/manure evaporation (20%): Some nitrogen turns to gas and drifts into the air, then falls back down in rain or snow.
• Manure (12-19%): The issue is bigger in the Raccoon River (19%) than the Des Moines River (12%) because of the prevalence of farms in northwest Iowa.
• Cities and towns (1.5-2%): Urban pollution like golf courses and car washes.

Iowa's extensive drainage tile system, which moves water off fields quickly, makes the problem especially acute. The state's agricultural infrastructure is designed for efficiency, but that same efficiency carries nitrates into rivers and streams.

Why is it hard to track fertilizer use on farms?

While synthetic fertilizer is the largest driver behind the rivers' nitrate levels, agriculture runoff is exempt from Clean Water Act permitting requirements. That makes it difficult to discern how much fertilizer is being applied on individual farms, says Michael Schmidt, general counsel for the Iowa Environmental Council.

'That is kind of a black box,' Schmidt says, noting the public knows how much gets sold each year, but not where it's going.

This regulatory gap means Iowans have limited visibility into exactly where fertilizer is being applied and how much is entering waterways.

Are corporate farms or family farms the bigger problem?

The report also examined the question of corporate versus family-owned farms. The answer is more nuanced than a simple comparison. Many large farms in Iowa are family-owned LLCs, and there isn't an easy apples-to-apples nitrate comparison between crop-focused farms versus livestock operations.

In general, nonfamily corporate farms own less land than family farms, but they're more likely to specialize in intensive livestock production, according to Iowa State University research. Two-thirds of the state's manure comes from operations with 1,000 or more animal units, based on the Iowa Department of Natural Resources' 2026 Animal Feeding Operations database.

What is Iowa doing to reduce nitrates?

While the state has a strategy to reduce nitrates and farmers are trying their best to properly apply fertilizer, they're also working in a larger system that incentivizes maximum production, Schmidt says.

The challenge for Iowa is balancing agricultural productivity with water quality. Farmers face economic pressure to maximize yields, and the current system rewards that behavior. The report's findings suggest that addressing nitrate pollution will require a focus on fertilizer application practices, not just on urban sources that contribute a fraction of the problem.

What does this mean for Des Moines water customers?

For residents of central Iowa, the report underscores that the water coming out of their taps is shaped primarily by agricultural practices upstream. Des Moines Water Works has spent millions on nitrate removal facilities over the years, costs that are ultimately borne by ratepayers.

The report's data gives policymakers and the public a clearer picture of where to focus efforts. With synthetic fertilizer as the dominant source, any meaningful reduction in nitrate levels will need to address how fertilizer is applied across Iowa's farmland.

As Iowa continues to debate water quality policy, this report provides a factual foundation for those discussions. The numbers are clear: agriculture drives the problem, and solutions will need to come from the farm field, not the city street.