An analysis from Environmental Working Group (EWG) mapped 15,309 animal feeding operations in Iowa, which is several thousand more than what is tracked and monitored by the state.
The group utilized satellite and aerial imagery to map animal feeding operations across Iowa and estimate the amount of manure they produce.
The report also notes a nearly 13 percent increase, from 2019 to 2025, in the number of animal feeding operations that have 1,000 or more animal units.
Animal units are based on live animal weight, with a set approximation for 1,000 pounds for each type of livestock. For example, 1,000 animal units is equivalent to: 2,500 hogs weighing more than 55 pounds, or 30,000 layer hens or 1,000 head of cattle.
Environmental Working Group estimated that in 2025 animals at Iowa feeding operations with more than 50 animals produced over 107 million tons of manure. The group alleges this manure, which is often applied to nearby crop land, has contributed to nitrate pollution in Iowa’s streams and rivers.
Mapping Iowa’s animal feeding operations
Anne Schechinger, senior director of agriculture and climate research at EWG and co-author of the analysis, said the research started with Iowa Department of Natural Resources animal feeding operation data that included operations with 300 animal units or more.
From there, EWG researchers used aerial imagery from the U.S. Department of Agriculture’s National Agriculture Imagery Program and satellite imagery from Google Earth to verify each operation in the DNR data and note if it appeared to be an active operation.
Schechinger said the researchers then combed through the imagery across the entire state to identify active animal feeding operations large enough to house 50 or more animals. A methodology using visual cues, like the type of barn structures, feeders and size, allowed EWG to determine the animals housed at the operation. Then, a geospatial software traced the size of the buildings to estimate the number of animals housed at the operation.
These points were then plotted on an interactive map to show the spread of animal feeding operations.
Based on the mapping, Sioux, Lyon, Plymouth, O’Brien and Washington Counties had the greatest concentrations of animal feeding operations. These five counties accounted for nearly one fifth of the facilities mapped across the state.
The analysis found that the vast majority, 66 percent, of animal feeding operations in the state raised hogs. It estimates the 10,172 facilities mapped had around 33.4 million hogs. The analysis found 4,801 cattle operations, with an estimated 2.7 million cattle and 336 poultry facilities housing 178.6 million turkeys and chickens.
Manure
The EWG analysis estimated animals at these facilities in 2025 produced the equivalent of 33 tons of manure for every person in the state, or a total of 107.6 million tons.
The largest livestock production facilities also produced the greatest share of manure, according to the report. While large feeding operations — those with 1,000 animal units or more — accounted for 29 percent of all facilities in the state, they generated 60 percent of the total estimated waste.
Facilities with 300 to 999 animal units — classified as medium facilities — comprised 51 percent of total facilities and 35 percent of manure. Small facilities, or those with fewer than 300 animal units, accounted for 20 percent of total facilities and 5 percent of manure.
Comparing the recent map to a 2020-released analysis of large animal feeding operations in the state, EWG found a 12.9 percent increase in large confined animal feeding operations.
“This expansion between 2019 and 2025 reflects the continued consolidation of livestock production into larger, more intensive facilities with greater waste management and drinking water challenges,” the report said.
Livestock producers must keep track of the amount of manure produced on their operations and how much was applied as fertilizer to nearby fields. This is all part of a manure management plan which is overseen by the Iowa Department of Natural Resources.
Animal feeding operations with fewer than 500 animal units, however, are not required to maintain manure management plans in Iowa.
Schechinger said while smaller operations are left out of state counts and of manure management requirements, those operations still produce manure and most likely apply it to nearby fields.
“Especially given the fact that Iowa has over 15,000 facilities in the state, a small operation next to a large operation can really have an impact on water quality when they’re both applying manure,” Schechinger said.
Iowa’s manure management program is often criticized by environmental groups as having low enforcement, but livestock producers say the plans are precise and that the high cost of fertilizer keeps farmers from applying above the nutrient budgets of their fields.
Schechinger said that based on the concentration of animal feeding operations in some parts of the state, it is “very, very likely” that the fields in those areas are being over applied with manure, especially since it is expensive and difficult to transport manure to fields further away. She suggested county-level oversight of these plans, rather than state level enforcement could help monitor and manage how much manure is applied.
Nutrients in the water
The nutrients in manure, and any fertilizer, are either absorbed into the field by the plants and the soil, or washed off of the field into a watershed. The analysis pointed to manure runoff as a contributing factor to high concentrations of nitrate in Iowa streams and to algal blooms in Iowa lakes.
The natural breakdown of organic matter, human waste and commercial fertilizers are additional causes of high nitrate levels that have made it difficult for Iowa water systems across the state to provide clean drinking water. These other factors, including the application of commercial fertilizer which do not have to be reported to the state, also contribute to excess nutrients in Iowa lakes.
EWG holds that nitrate concentrations in drinking water at levels far below the U.S. Environmental Protection Agency maximum of 10 milligrams per liter, are linked to increased risk of certain cancers, thyroid disease and birth defects.
“It doesn’t matter where it’s coming from if it’s getting in the drinking water,” Schechinger said. “It’s hazardous for our health, it’s expensive for water utilities to remove, so it’s really important to be reducing total nitrogen from fertilizer or from manure that’s being applied to fields in the state.”
The environmental group suggested consumers reduce their consumption of meats raised at “factory farms” by shopping for proteins with grass fed, pasture raised or certain types of humane labels, to reduce the “environmental and public health damages caused by raising livestock” in animal feeding operations.
It also pushed for policy changes to conservation programs to prioritize practices like cover crops or stream-side buffers, rather than manure storage systems which the group has previously found make up a significant portion of USDA’s Environmental Quality Incentives Program awards.
As water quality continues to be a top concern for Iowans, the state launched a 12-year $319 million water quality program to monitor, upgrade treatment plants and supply additional conservation incentives to farmers in certain regions of the state.
The package was approved by the legislature and signed by Gov. Kim Reynolds in the spring. Initial rounds of the conservation incentives have opened to farmers.
Schechinger said Environmental Working Group hopes to continue researching the spread of manure in Iowa, possibly with modeling that would gather more information about field application in the state.
Additionally, EWG plans to release a similar analysis of animal feeding operations in North Carolina, and has previously conducted the same analysis in Minnesota.
Cami Koons covers agriculture and the environment for Iowa Capital Dispatch, where this story first appeared.
