Study: 72% of Illinois wetlands no longer protected by federal Clean Water Act
Other states likely face similar losses of federal status
University of Illinois at Urbana-Champaign, News Bureau
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The research team included, clockwise from front center, Chelsea Peterson, Jessica Monson, Geoffrey Pociask, Paul Marcum, Julie Nieset and Jeffrey Matthews.
view moreCredit: Photo by Fred Zwicky
CHAMPAIGN, Ill. — Illinois once harbored more than 8 million acres of wetlands. By the 1980s, all but 1.2 million wetland acres had been lost, filled in for development or drained to make way for agriculture. Now, thanks to a 2023 Supreme Court decision, roughly 72% of the remaining 981,000 acres of Illinois wetlands are no longer protected by the federal Clean Water Act, putting communities at risk of losing the flood control, groundwater recharge, water purification and natural habitat these wetlands provide, researchers report.
A patchwork of state and county-level wetland regulations offer some protection to those acres, but most are unprotected, the researchers found. Their study is detailed in the Journal of Environmental Management.
The 2023 Sackett v. Environmental Protection Agency decision followed decades of shifting guidance on the 1972 Clean Water Act. In 1985, “the U.S. Supreme Court unanimously held that wetlands adjacent to traditionally navigable waters are ‘waters of the United States’ and therefore protected by the Clean Water Act,” the researchers wrote. That ruling allowed federal agencies to prevent the destruction of millions of acres of wetlands across the nation and preserve their natural functions.
But later Supreme Court rulings chipped away at that more inclusive definition of federally protected waters, culminating in the 2023 Sackett decision, which significantly narrowed the types of wetlands that were federally protected.
“The Sackett decision required that wetlands have a continuous surface connection to ‘relatively permanent waters’ of the United States and be indistinguishable from those waters,” said University of Illinois Urbana-Champaign graduate student Chelsea Peterson, who led the new analysis with U. of I. natural resources and environmental sciences professor Jeffrey Matthews. “That removes protections from wetlands that flood infrequently, have surface connections to nonpermanent streams or are spatially isolated from permanent streams, which could be due to levees or dry land.”
The requirement of a surface connection to relatively permanent waters is problematic, said study co-author Jessica Monson, a research scientist at the Illinois State Geological Survey.
“The concern is that it’s not really addressing the hydrologic connections that occur below the land surface,” she said.
It also removes protections for wetlands that may better mitigate a storm surge or heavy rain event. Unprotected wetlands in Illinois are estimated to provide $419 million in residential flood control benefits.
“Their value for flooding actually comes from the fact that they’re not saturated all the time,” Peterson said.
“Water supply is another function that wetlands provide,” said study co-author Geoffrey Pociask, a wetlands geologist at the ISGS. “Some of those wetlands further up the watershed not only capture and process contaminants but also recharge our aquifers.”
Beyond serving as natural water filters and collectors, wetlands are vital habitats for a host of species.
“Some species are adapted to the fluctuating water levels,” Peterson said. Amphibians like salamanders may do better in a wetland that is not inundated all the time because there are fewer predators like fish. Nearly 50% of threatened and endangered plant and animal species in the U.S. live in wetland habitats, the team reports.
To gain a clearer understanding of the statewide implications of the 2023 Sackett decision, the researchers had to consider how the ruling might be interpreted.
“We varied three physical parameters that could influence to what extent a wetland has a ‘continuous surface connection’ to the waters of the United States,” the researchers wrote. These included spatial distance, flood frequency and flow permanence requirements. They calculated the impact of several different scenarios to account for uncertainty in agency rules.
The analysis revealed that 72% of Illinois’ wetlands are no longer considered waters of the United States and therefore not protected by the Clean Water Act.
Some of these “non-WOTUS” wetlands are protected by state and/or county-level regulations, the team found. Eight counties in the Chicago region, for example, regulate activity in wetlands through their stormwater management ordinances. A state law also requires compensation for wetland acreage developed with state funding.
Up to 563,000 acres of Illinois wetlands lie outside any county, state or federal protection, the researchers found. This represents about 80% of the wetlands that are no longer protected under the Clean Water Act.
The team compared a map of unprotected wetlands with a map of county-level risks from climate-related hazards, finding the regions in Illinois that are the most at risk, particularly from floods. These include the Moline-Rock Island-Burlington region near the lower Rock River, the Peoria metropolitan area surrounding the Illinois River, the Grafton-Alton-East St. Louis region near the confluence of the Missouri and Mississippi Rivers, and the Cape Girardeau-Cairo region near the convergence of the Ohio and Mississippi Rivers.
“The potential losses go beyond a wetland’s ecological, recreational and aesthetic benefits,” said Pociask, who referred to another recent study finding that each wetland acre provides about $750 in flood-protection benefits annually. “Wetlands offer a kind of natural insurance against potentially catastrophic losses.”
“These also are real losses in flood damages, crop damages,” he said. “And those are people losing homes and businesses, losing money.”
“Originally, about 22% of the land area of Illinois was wetlands,” said study co-author Paul Marcum, a research scientist at the Illinois Natural History Survey. “That went down to about 2.6% by 2023. With the Sackett decision, much of that remaining wetland acreage is at risk.”
The findings point to the importance of municipal and county-level ordinances that preserve wetlands, the researchers wrote.
INHS research scientists Julie Nieset and Brian Wilm, also contributed to the study. The ISGS and INHS are divisions of the Prairie Research Institute at the U. of I.
The U.S. Environmental Protection Agency funded this research.
The paper “A national policy with local consequences: Quantifying the downstream effects of Sackett on Illinois wetlands and communities” is available online.
DOI: 10.1016/j.jenvman.2025.126931
Wetlands, like those of Round Pond Swamp in Pope County, Ill., perform a variety of functions for communities, from recreation to stormwater management and wildlife habitat, the team reports.
Credit
Photo by Paul B. Marcum
Ephemeral wetlands, like Busey Woods in Champaign County, Ill., are not saturated year-round and so have the capacity to absorb storm water surges in the rainy seasons, protecting communities from flooding.
Credit
Photos by Fred Zwicky and Diana Yates
Two deer rest in a low area of Busey Woods.
Credit
Photo by Fred Zwicky
Journal
Journal of Environmental Management
Method of Research
Data/statistical analysis
Subject of Research
Not applicable
Article Title
A national policy with local consequences: Quantifying the downstream effects of Sackett on Illinois wetlands and communities
