Aerial view of a wetland with water and trees
New WOTUS Definition to Have Ripple Effect on Projects

On January 18, 2023, the Environmental Protection Agency (EPA) and the United States Army Corps of Engineers (USACE) published a new definition of “waters of the United States” (WOTUS) to the Federal Register. The final rule, "Revised Definition of ‘Waters of the United States,’" expands the scope of federal jurisdiction under the Clean Water Act (CWA) and is largely founded on the pre-2015 interpretation of WOTUS. The new rule goes into effect on March 20, 2023.


Congress passed the CWA in 1972, thereby establishing federal jurisdiction and regulatory authority over WOTUS. Congress did not precisely define this phrase, however, and instead left that responsibility to EPA and USACE. Lacking a precise statutory definition of WOTUS, the agencies have struggled to adopt straightforward regulations for implementing the CWA.

Two Supreme Court decisions in the 2000s introduced further regulatory uncertainty. In 2006, Rapanos v. United States resulted in a split decision where Justice Antonin Scalia argued the CWA only applied to waterbodies “with a continuous surface connection” to navigable waters, whereas Justice Anthony Kennedy argued the CWA applied to any waterbodies that “affect the chemical, physical, and biological integrity of other covered waters” as evidenced by a “significant nexus” test.

In the wake of Rapanos, the agencies issued non-binding guidance in 2008 to implement Kennedy’s “significant nexus” test. However, the guidance failed to resolve many questions concerning the scope of federal jurisdiction and prompted arduous case-by-case analyses of whether the CWA applied to certain waterbodies.

Amid persistent uncertainty in the post-Rapanos landscape, the agencies issued the Clean Water Rule in 2015 to circumscribe federal jurisdiction under the CWA. Among other changes, the 2015 rule specified which kinds of waterbodies would automatically receive protection under the CWA, exempted certain kinds of waterbodies from regulation and identified which waterbodies still required case-by-case analyses. However, litigation and court orders delayed and constrained the implementation of the 2015 rule. When it eventually took effect in 2018, the Clean Water Rule applied in just 22 states, leaving other states bound to earlier versions of the regulations or awaiting direction from the courts. Despite its attempt at clarification, the 2015 rule ultimately created a confusing geographic mosaic of CWA jurisdiction.

It was against this backdrop that Executive Order 13778 was issued in 2017, which directed the agencies to repeal and replace the Clean Water Rule of 2015. The agencies completed their repeal of the Clean Water Rule in December 2019 and replaced it with the April 2020 Navigable Waters Protection Rule (NWPR), which narrowed the scope of federal jurisdiction under the CWA. In August 2021, the 2020 NWPR was vacated and remanded in response to EPA and USACE’s receipt of the U.S. District Court for the District of Arizona’s order in the case of Pascua Yaqui Tribe v. U.S. EPA. On December 30, 2022, the final “Revised Definition of ‘Waters of the United States’” rule was announced and the new rule was published a few weeks later in the Federal Register.

What’s included under the new WOTUS definition?

The new rule is reminiscent of pre-2015 WOTUS interpretations and includes revisions that take into account Supreme Court precedent. The new WOTUS definition includes:

(a)(1) Traditional navigable waters, the territorial seas, and interstate waters

(a)(2) Impoundments of "waters of the United States"

(a)(3) Tributaries to traditional navigable waters, the territorial seas, interstate waters, or impoundments of the "waters of the United States" when the tributaries meet either the "relatively permanent standard" or the "significant nexus standard" (jurisdictional tributaries)

(a)(4) Wetlands adjacent to traditional navigable waters, the territorial seas, and interstate waters; wetlands adjacent to and with a continuous surface connection to relatively permanent impoundments of the "waters of the United States" or adjacent to tributaries that meet the "relatively permanent standard"; and wetlands adjacent to impoundments of the "waters of the United States" or jurisdictional tributaries when the wetlands meet the "significant nexus standard."

(a)(5) Intrastate lakes and ponds, streams, or wetlands not identified in the above categories and that meet either the "relatively permanent standard" or the "significant nexus standard."

What does “relatively permanent standard” mean?

The new definition states that the “relatively permanent standard” refers to the test used to identify relatively permanent water bodies. To meet "relatively permanent standard," water bodies must be relatively permanent, standing, or continuously flowing waters connected to traditional navigable waters, the territorial seas, and interstate waters; or waters with a continuous surface connection to such relatively permanent waters or to traditional navigable waters, the territorial seas, and interstate waters.

What does “significant nexus standard” mean?

The “significant nexus standard” refers to the test to identify waters that, either alone or in combination with similarly situated waters in the region, significantly affect the chemical, physical, or biological integrity of traditional navigable waters, the territorial seas, or interstate waters. The rule defines “significantly affect” as having a material influence on the chemical, physical, or biological integrity of an (a)(1) water. Under this definition, waters are evaluated either alone or in combination with other similarly situated waters in the region based on the functions the waters will perform. This rule identifies specific functions that will be assessed when determining whether a function provided by the water has a material influence on the integrity of an (a)(1) water. These functions include water conveyance, flow rate, trapping, filtering, transport of materials (including nutrients, sediment, and other pollutants), temperature modulation, or provision of habitat and food resources for aquatic species. Factors that may affect the identified beneficial functions include the distance from (a)(1) waters; hydrologic factors such as frequency, duration, magnitude, timing, and rate of hydrologic connections, including shallow subsurface flow; the size, density, or number of similarly situated waters; landscape position and geomorphology; and climatological variables such as temperature, rainfall, and snowpack. Of these factors, distance and hydrology are the key factors in a significant nexus determination.

Does the rule contain any exclusions?

The final rule notes several WOTUS exclusions, including:

  1. Waste treatment systems, including treatment ponds or lagoons, designed to meet the requirements of the CWA
  2. Prior converted cropland designated by the Secretary of Agriculture (exclusion ceases upon a change of use)
  3. Ditches (including roadside ditches) excavated wholly in and draining only dry land and that do not carry a relatively permanent flow of water
  4. Artificially irrigated areas that would revert to dry land if the irrigation ceased
  5. Artificial lakes or ponds created by excavating or diking dry land to collect and retain water used for such purposes as stock watering, irrigation, settling basins, or rice growing
  6. Artificial reflecting or swimming pools or other small ornamental bodies of water created by excavating or diking dry land to retain water for primarily aesthetic reasons
  7. Waterfilled depressions and pits created in dry land incidental to construction activity and pits excavated in dry land to obtain fill, sand, or gravel unless and until the construction or excavation operation is abandoned and the resulting body of water meets the WOTUS definition; and
  8. Swales and erosional features (e.g., gullies, small washes, etc.) characterized by low volume, infrequent, or short duration flow.

What are the most notable changes to the WOTUS definition?

The revised WOTUS definition includes a few notable changes from the pre-2015 CWA interpretation.

  1. Traditional navigable waters, interstate waters, and the territorial seas have been combined into the (a)(1) category. In the pre-2015 definition, these waters were split into three separate categories. Previously, these three categories were exempt from both the ‘relatively permanent standard’ and the ‘significant nexus standard’. Once combined, these (a)(1) waters remain exempt from both standards. No change to policy or approach is associated with this difference but rather, this change identifies all water bodies automatically defined as WOTUS regardless of relative permanency and significant nexus.
  2. All water bodies which do not fall into the (a)(1) category must meet either the ‘relatively permanent standard’ or the ‘significant nexus standard’. Their effect on interstate or foreign commerce is no longer a factor.
  3. Tributaries (and adjacent wetlands) to impoundments and waters not identified as (a)(1) water bodies (‘other waters’) are evaluated based only on their relationship to an (a)(1) water, not the impoundment or ‘other water’.
  4. Continuous surface connection is no longer limited to abutting. Under the ‘relatively permanent standard’ for wetlands, wetlands meet the continuous surface connection if they physically abut, or touch a relatively permanent impoundment or a jurisdictional tributary or if they are connected to these waters by a discrete feature. These discrete features include non-jurisdictional ditches, swales, pipes, and culverts. These features can also include man-made dikes or barriers, natural river berms, beach dunes, and other, similar features provided that there is evidence of a continuous surface connection as waters separated by these structures may continue to have a hydrologic connection either through seepage or overtopping.
  5. Exclusions do not apply to (a)(1) waters.

What does the expanded WOTUS definition mean for projects?

Organizations with operations that interface with potential WOTUS should familiarize themselves with the new definition and assess potential impacts, such as more complex permitting processes and/or more stringent discharge limitations. Previously identified WOTUS may need to be re-evaluated under the new definition and new jurisdictional determinations for previously excluded waters may be required. Upon its effective date, this new WOTUS definition may impact project permitting requirements and environmental compliance with the CWA. Any project with the potential to impact nearby waters may now face new requirements and should account for additional lead time and project costs associated with current or future permitting activities.

Anything else I should know?

Yes, the new WOTUS definition largely hinges on a Supreme Court decision expected in June 2023. In Sackett v. EPA, the Supreme Court will decide whether wetlands without a continuous surface water connection to regulated waters may themselves be regulated as WOTUS. If the Supreme Court determines that wetlands must have a continuous surface water connection to regulated waters to be regulated as WOTUS, the "significant nexus standard" for wetlands in the new definition would be rendered moot, reducing EPA jurisdiction over many previous WOTUS. Within the published “Revised Definition of ‘Waters of the United States,’” the EPA noted that the upcoming Supreme Court decision is not a direct challenge to any rules defining WOTUS. From this statement, it appears that the agencies do not anticipate any impact on the new WOTUS definition. At this time, it is unclear what action will be taken by the agencies if the Supreme Court issues a decision favoring Sackett but there is the possibility that additional rulemaking may be required.

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Margaret Caligaris headshot
Margaret Caligaris
Environmental Compliance & Permitting Specialist, San Luis Obispo, CA

Margaret is an environmental compliance and permitting specialist with over 4 years of experience in natural resource planning and permitting. She specializes in waters regulation, permitting, and stormwater compliance.
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