Groups interested in the EPA/Army Corps of Engineers’ proposal to rewrite the definition of “waters of the United States” — and there are many — are struggling to get a handle on its impacts.

EPA and the Corps say they can’t put a percentage on the extent of waters and wetlands that would not be covered by the Feb. 14 proposal, which carries an April 15 comment deadline. (Many groups and Democratic lawmakers have asked EPA and the Corps to extend the comment period.)

Acting EPA Administrator Andrew Wheeler has consistently said any estimates of waters left unprotected by federal regulations are not reliable, labeling as “misinformation” reports that up to 60 percent of streams could lose protection under the proposal.

“There is no nationwide map that identifies ‘waters of the United States,’” he said at the rollout of the proposal Dec. 11. In supplemental materials released at the same time, the agencies said they were “not aware of any means to quantify changes in (Clean Water Act) jurisdiction with any precision that may or may not occur as a result of this proposed rule.”

The agencies also said they didn’t know “of any map or dataset that accurately or with any precision portrays the scope of CWA jurisdiction at any point in the history of this complex regulatory program. Establishing a mapped baseline from which to assess regulatory changes is likewise impracticable at this time.”

Andrew Wheeler

EPA Acting Administrator Andrew Wheeler

But EPA itself put some numbers on the impacts back in 2017 when the proposal was under discussion at the agency. In slides that have since become public through a Freedom of Information Act request by E & E Publishing, the agency cited data from the U.S. Geological Survey and Fish and Wildlife Service to note that ephemeral streams, which would not be covered by the proposal, make up 18 percent all streams nationwide; wetlands that do not abut already jurisdictional waters — and which also would be unregulated — make up approximately 51 percent of the nation’s wetlands.

Intermittent, or seasonal, streams, according to the same slides, make up 52 percent of streams nationwide. Those types of waterways are covered under the proposal, but the agencies are asking for comments on whether they should regulate streams that have less than intermittent flow, or whether they should limit their jurisdiction to perennial streams only. Ephemeral waters only flow in response to rainfall or snowfall.

The complicated nature of the proposal has left groups preparing comments scrambling to assess its impacts.

“We will pull as much as we can together in 60 days,” said Geoff Gisler, a senior attorney at the Southern Environmental Law Center and the leader of its Clean Water Program. Gisler acknowledges that data from USGS’s National Hydrography Dataset, which EPA and the Corps used in their analyses, does not align with data on jurisdictional waters. But he adds, “It’s not fair to just throw up our hands and say we can’t project the effects of this rule.”

Geoff Gisler

Geoff Gisler, SELC

Gisler estimates roughly 40-50 percent of streams could lose federal jurisdiction under the proposal. He also says coastal plain wetlands are vulnerable, as are perennial streams if they do not contribute adequate flow to navigable waters.

Kyla Bennett, director of Public Employees for Environmental Responsibility's New England office, put the percentage of vulnerable waterways at 60-90 percent. She said she arrived at the figures based on EPA documents, discussions with current and former federal employees who have worked on wetlands, and her own experience — she has a Ph.D. in ecology and worked for 10 years at EPA doping permitting and wetlands enforcement.

“EPA has an obligation to estimate the losses,” Bennett said in an email. “Wheeler cannot simply say that these statements are invalid when his own agency says that incomplete data show a loss of 18 percent of streams and 51 percent of wetlands. This is a huge underestimate, and EPA knows it.”

One recently-released analysis of three watersheds in Minnesota, Oklahoma and New Mexico concluded that “a narrower definition of jurisdictional waters proposed by the current administration will have a significant impact on the protection of wetlands and waters nationwide.” The analysis also noted “risk is more pronounced for ephemeral and isolated wetlands such as those found in semiarid environments and the glaciated prairie pothole region of the U.S.”

The analysis by GeoSpatial Services (GSS) at St. Mary’s University of Minnesota did not attempt to quantify the impacts of the proposal nationwide, but did find the number of non-jurisdictional wetlands and stream miles increased markedly under the two scenarios closest to the parameters of the proposed rule.

“More accurate modeling of the final proposed rulemaking can be achieved as additional details become available from the EPA and (Army Corps of Engineers),” the GSS report said. GSS Executive Director Andy Robertson says he lacks the funding for a nationwide analysis.

EPA has not decided whether to extend the comment period, which is due to end April 15. When the proposal was announced, Wheeler said 60 days was enough time.

American Farm Bureau Federation spokesman Mace Thornton said it's been difficult to assess the benefits of the proposal because of the vagueness of the 2015 rule that came before. The Feb. 14 proposal, he said, is "an improvement in clarity for both companies and regulators."

For more news, go to