Another Definition of Waters of the United States (WOTUS)

On November 20, 2025, the Army Corps of Engineers (“Corps”) and the Environmental Protection Agency (“EPA”) released a draft updated definition of “waters of the United States” (“WOTUS”). This draft continues a back and forth that began under the Obama administration and has been repeated under each administration since.

The tug of war began when the United States Supreme Court issued a fractured ruling in 2006. The ruling failed to get a majority, with the justices splitting 4-4-1. The Obama administration began the series of competing definitions with a rule that became effective in 2015. Subsequent administrations have each issued their own updates.

The latest iteration seeks to conform the rule to the United States Supreme Court decision in Sackett v. Environmental Protection Agency, 598 U.S. 651 (2023). The proposed rule deletes the interstate waters category and deletes “intrastate” from the lakes and ponds category. The agencies also propose to add definitions of “continuous surface water connection,” “ditch,” “prior converted cropland,” “relatively permanent,” “tributary,” and “waste treatment system.”

Most importantly for the groundwater industry, the proposed rule adds back the groundwater exclusion in paragraph (B)(9), which excludes “[g]roundwater, including groundwater drained through subsurface drainage systems” from the definition of WOTUS. This identical exclusion was included in the rule issued by the Obama administration and the first Trump administration, but was removed in the rule promulgated under the Biden administration.

Although the reasoning is not completely clear, the Biden administration removed the exclusion because of uncertainty presented by the United States Supreme Court ruling in County of Maui v. Hawaii Wildlife Fund (2020). In that case, the Court found that deposits of pollutants into groundwater could be regulated under the Clean Water Act if the pollutants make their way to waters of the United States.

Although the County of Maui does not address the definition of waters of the United States, the decision creates uncertainty with respect to federal regulation of groundwater pollution, which is traditionally left to the states. Although the groundwater exclusion is back in the definition of WOTUS, the uncertainty from County of Maui remains as well.

Background

The Clean Water Act covers discharges into “navigable waters”. Congress defined “navigable waters” as “waters of the United States,” leaving the rest to the Environmental Protection Agency and Corps of Engineers, who jointly administer the permitting program. Waters that are in fact navigable are clearly WOTUS. The regulations (developed by the EPA and Corps) also define tributaries of navigable waters and “adjacent wetlands” as WOTUS. If the “water” or wetland is determined to be WOTUS, no pollutants or dredge and fill material can be discharged without a permit.

Disputes have arisen over what constitutes “waters of the United States,” particularly whether intermittent and ephemeral streams, ditches and the like are included. The United States Supreme Court, in 2006, had come up with two different definitions, with one group of justices focusing on “relatively permanent, standing, or continually flowing bod[ies] of water,” and Justice Kennedy developing the “substantial nexus” test. The substantial nexus test is very subjective and potentially includes groundwater as WOTUS.

Rules developed under the Obama administration and the Biden administration essentially defined waters falling under either category as WOTUS. The rule promulgated under the first Trump administration, in contrast, attempted to limit the definition of WOTUS to “relatively permanent, standing, or continually flowing bod[ies] of water.”

In Sackett, the United States Supreme Court, in a unanimous decision, rejected the “substantial nexus” test and found that “waters” in “waters of the Untied States” refers to “geographic[al] features that are described in ordinary parlance as ‘streams, oceans, rivers and lakes.’”

The justices split, however, on when wetlands should be considered WOTUS. The 5-justice majority found that wetlands must be “adjacent” to actual WOTUS to be considered WOTUS. The majority also defined adjacent wetlands as those wetlands that are “indistinguishable” from WOTUS due to a “continuous surface water connection.” A continuous surface water connection means that the wetlands abut the WOTUS.

The Biden Administration Revised Rule

In response to Sackett, the Biden administration quickly revised its recently adopted WOTUS rule. The revised rule deleted all references to the substantial nexus test, leaving only waters that are relatively permanent, standing, or continually bodies of water as potentially included as WOTUS. Second, the revised rule redefines “adjacent” as “having a continuous surface connection.” In addition, “interstate wetlands” are deleted from the definition, leaving “interstate waters.” So far, so good. The changes remained true to the Sackett decision.

However, the fact that the revisions stopped there raised questions. First, the drafters inexplicably failed to define “waters”. The Sackett decision clearly dictates a definition of waters as “relatively permanent, standing, or continually flowing bod[ies] of water.” The failure to include that definition means that “interstate waters” could include intermittent or ephemeral streams that cross state lines. The Sackett court clearly did not intend that result.

Second, the revised rule failed to define “continuous surface connection.” Although the short time period and lack of public comment period may have prevented inclusion of this definition, the Sackett decision included some clear signals. A continuous surface connection exists where the wetland is “indistinguishable” from the adjacent water, “making it difficult to determine where the ‘water’ ends, and the ‘wetland’ begins.

Finally, and perhaps understandably, we were left wondering about what water bodies constitute “tributaries.” Although the revised definition makes clear that a tributary must be a relatively permanent, standing or continually flowing body of water, uncertainty remained.

The Latest Proposed Rule

The latest proposed rule seeks to conform the rule more fully to the United States Supreme Court decision in Sackett v, Environmental Protection Agency, 598 U.S. 651 (2023). The proposed rule deletes the interstate waters category, deletes “intrastate” from the lakes and ponds category. The agencies also propose to add definitions of “continuous surface water connection,” “ditch,” “prior converted cropland,” “relatively permanent,” “tributary,” and “waste treatment system.” Most importantly for the groundwater industry, the proposed rule adds back the groundwater exclusion in paragraph (B)(9), which excludes “[g]roundwater, including groundwater drained through subsurface drainage systems” from the definition of WOTUS. This language is identical to the language excluding groundwater in prior definitions.

“Continuous surface connection” is defined as “having surface water at least during the wet season and abutting (i.e., touching) a jurisdictional water.” “Ditch” means a “constructed or excavated channel used to convey water.” “Relatively permanent” means “standing or continuously flowing bodies of surface water that are standing or continuously flowing year-round or at least during the wet season.” Note that the definition limits relatively permanent waters to “surface water.” The definition of “tributary” focuses on relatively permanent flow and the requirement of a connection to a traditional navigable water body, either directly or through water features that include relatively permanent flow.

The Groundwater Exclusion

The groundwater exclusion brings back an exclusion that first appeared in the regulations in the rule promulgated under the Obama administration that became effective on August 28, 2015. The Navigable Waters Protection Rule, promulgated under the Trump administration, and that became effective on June 22, 2020, repeated the groundwater exclusion verbatim from the earlier rule. In each of these rules, “groundwater, including groundwater drained through subsurface drainage systems” was excluded from the definition of WOTUS. Note that “drained through subsurface drainage systems” should be interpreted as “drained through [artificial] subsurface drainage systems” like tile systems that midwestern farmers use.

However, the Biden administration rule, effective on March 20, 2023, eliminated the groundwater exclusion. A footnote confirmed that the federal government never interpreted groundwater to be a “water of the United States” under the Clean Water Act. The footnote cited County of Maui v. Hawaii Wildlife Fund, 140 S. Ct. 1462 (2020). to support this interpretation, noting that the United States Supreme Court explained that Congress “left general groundwater regulatory authority to the States…” The footnote went on the explain while groundwater itself is not waters of the United States, discharges of pollution to groundwater may require a National Pollution Discharge Elimination (NPDES) permit if the pollution reaches jurisdictional surface water (also citing Maui County).

The Impact of Maui County

In April of 2020, the United States Supreme Court issued their opinion in County of Maui v. Hawaii Wildlife Fund. Water Systems Council filed a friend of court brief in this case. The case involved the question of whether and when indirect discharges of pollutants require a National Pollution Discharge Elimination System (NPDES) permit. In this case, the discharge traveled through groundwater prior to reaching the ocean.

The United States Supreme Court set forth a new standard for determining when a source needs an NPDES permit: “the statute requires a permit when there is a direct discharge from a point source into navigable waters or when there is the functional equivalent of a direct discharge.”  Recognizing that this statement “does not … clearly explain” when a source may need an NPDES permit, the Court set forth “some of the factors that may prove relevant” in any given case. However, these factors did not clarify the test and still cause confusion in the courts.

In summary, the possibility that discharges to groundwater that may eventually reach waters of the United States are regulated under the Clean Water Act creates uncertainty. Although “waters of the United States” and “discharge” are two different issues under the Clean Water Act, Maui County may allow regulation of groundwater at the federal level in a way that strongly resembles making groundwater WOTUS.

Takeaways from the Proposed Rule

(1)  Assuming that the proposed rule is finalized, groundwater is clearly not WOTUS. The Sackett decision made that conclusion clear and this rule would explicitly exempt groundwater from WOTUS.

(2)  The rule adds some clarity with definitions of tributary, continuous surface connection, relatively permanent, ditch, and other key terms. The scope of WOTUS has been significantly narrowed. Intermittent and ephemeral streams are clearly not WOTUS at this point.

(3)  Although the rule makes explicit that groundwater cannot be considered WOTUS, the Maui County backdoor remains open. Litigation will now likely focus on the lack of clarity of the Maui County factors. Courts will have to determine in which situations where contaminants in groundwater make their way to WOTUS will be regulated under the Clean Water Act.