The Practical Application of the Significant Nexus Test: The Final Waters of the US Rule


This is my penultimate article on the Administration’s final Waters of the US rule. For those of you who have read our previous articles on the proposed and final rules (hi Mom!), you know we have concerns about the significant nexus test. Our concern is not just the breadth of the test, but its ambiguity and need for case-by-case application. For the regulated community, knowing when one must comply with the law is half the battle (at least). And the significant nexus test, based on neither science nor the language of the Clean Water Act, is an ambiguous, case-by case test.

But apart from its ambiguity, there is the practical reality – the practical difficulty – of actually applying the test. Now that the test has been ensconced into regulation, we’ll take a quick look at the practical implications of applying of the test.

As you’ll recall, the significant nexus test requires a determination of whether the water in question – alone or in aggregation with other similarly situated waters in the region – significantly affects the chemical, physical or biological integrity of a traditionally navigable or interstate water or the territorial sea (with “significant” meaning “more than speculative or insubstantial.”). The “region” is the watershed that drains to the nearest traditionally navigable or interstate water or the territorial sea, and waters are “similarly situated” when they function alike and are sufficiently close to function together in affecting downstream waters.

The reality of the Clean Water Act is that the onus is typically on the regulated community to show that a water is not jurisdictional. In a permitting situation, for example, it is incumbent on the permit applicant to delineate waters and wetlands and offer an explanation to the Corps as to which waters are not jurisdictional. In an enforcement setting, the alleged violator typically must make EPA (and the Corps) comfortable that the waters that were filled or polluted were not jurisdictional in order to reduce settlement demands and/or avoid prosecution. Thus, the permit applicant will usually face the onus of applying the significant nexus test.

This means that the applicant will need to:

That’s a long and onerous list. As we’ll discuss tomorrow in our last post, we think the practical implication of this reality will be that many permit applicants will choose to concede jurisdiction rather than spend the time and money trying to apply the significant nexus test.


© 2025 Bracewell LLP
National Law Review, Volume V, Number 159