In late August, a court in the District of Arizona issued a decision vacating the Navigable Waters Protection Rule (“NWPR”), the most recent regulation defining the term “waters of the United States” (“WOTUS”) under the Clean Water Act (“CWA”). Prior to the court’s decision, the Environmental Protection Agency (“EPA”) had announced that it would begin a rulemaking process to repeal the NWPR – which has only been in place since June, 2020 – and replace it with a new regulation redefining WOTUS. Since the court’s decision, EPA has announced that it will cease implementation of the NWPR and will instead interpret WOTUS consistent with the pre-2015 regulatory regime until further notice in order to comply with the court’s order. The pre-2015 regulatory regime is complex. It involves regulations adopted by EPA in the 1980s that define the term WOTUS, as well as memoranda issued by EPA in the 2000s regarding decisions from the United States Supreme Court that interpreted those regulations. The regulations, the Supreme Court decisions, and the subsequent memoranda must be reviewed in order to understand how EPA will be interpreting the term WOTUS until further notice.


The CWA was enacted by Congress in 1972 as the nation’s primary federal law regulating water pollution. The main goal of the CWA is to “restore and maintain the chemical, physical, and biological integrity of the Nation’s waters.” 33 U.S.C. § 1251. To do this, the CWA established a permitting program that prohibits an unpermitted discharge of any pollutant from a point source into “navigable waters.” 3. U.S.C. § 1342. Because permits for discharges are only required for those discharges made into navigable waters, the term is key to understanding which waters are subject to CWA jurisdiction. The text of the CWA defines the term navigable waters as “the waters of the United States, including the territorial seas.” 33 U.S.C. § 1362(7). However, the term WOTUS is not further defined in the statute. Instead, EPA, the federal agency tasked with administering the CWA, has been responsible for defining the term. Since 1972, EPA has redefined WOTUS several times. For a full timeline of the term’s definitions, click here.

The most recent definition of WOTUS was adopted by EPA in 2020. The NWPR was drafted, in part, due to multiple courts across the country preventing the implementation of the previous WOTUS definition which was adopted by EPA in 2015. The NWPR was narrower than the 2015 rule, limiting what was included in the definition of WOTUS to six categories of waterbodies. This was in contrast to the 2015 rule which was broad and required a case-by-case analysis for various types of waterbodies. The 2015 rule was itself a response to decisions from the United States Supreme Court interpreting the definition of WOTUS according to regulations EPA had passed in the 1980s.

Prior to formally adopted the NWPR, EPA had issued a final regulation repealing the 2015 rule. By doing so, EPA returned to the regulatory regime that had been in place before the 2015 rule was passed, meaning that for a limited period of time EPA was interpreting WOTUS according to the 1980s regulations and memoranda issued by the agency in response to Supreme Court decisions. When the Arizona district court vacated the NWPR, it caused the legal definition of WOTUS to revert to what it had been before the NWPR went into effect. This means that until EPA adopts a new WOTUS definition, or until it is ordered by a court to do differently, EPA will be interpreting WOTUS according to the 1980s regulations and accompanying memoranda. For more information on the Arizona decision, see here.

1980s Regulations

In 1980, EPA issued a final regulation to redefine WOTUS. This was only the second time that EPA had done so. By 1982, the Army Corps of Engineers (“Corps”), which administered the dredge and fill program under the CWA, had also adopted the 1980 definition.

According the 1980 rule, WOTUS is defined as:

(a) All waters which are currently used, were used in the past, or may be susceptible to use in interstate or foreign commerce, including all waters which are subject to the ebb and flow of the tide;
(b) All interstate waters, including interstate “wetlands;”
(c) All other waters such as intrastate lakes, rivers, streams (including intermittent streams), mudflats, sandflats, “wetlands,” sloughs, prairie potholes, wet meadows, playa lakes, or natural ponds the use, degradation, or destruction of which would affect or could affect interstate or foreign commerce including any such waters:

(1) Which are or could be used by interstate or foreign travelers for recreational or other purposes;
(2) From which fish or shellfish are or could be taken and sold in interstate or foreign commerce; or
(3) Which are used or could be used for industrial purposes by industries in interstate commerce;

(d) All impoundments of waters otherwise defined as waters of the United States under this definition;
(e) Tributaries of waters identified in paragraphs (1) – (4) of this definition;
(f) The territorial sea; and
(g) “Wetlands” adjacent to waters (other than waters that are themselves wetlands) identified in paragraphs (a) – (f) of this definition.

40 C.F.R. 122.2 (1981). Under this definition, some waters are more easily identifiable as falling under CWA jurisdiction than others. For example, it is obvious that the Mississippi River would qualify as a WOTUS because it has both been used to facilitate interstate commerce, and is an interstate water. Additionally, the Pacific Ocean would clearly be a WOTUS because it is a territorial sea. However, identifying waters that were located entirely within the boundaries of one state but still fell under the jurisdiction of the CWA because their degradation or destruction would affect waters that crossed state lines proved to be a challenge. Particularly when it came to wetlands. That confusion ultimately resulted in lawsuits that made their way to the United States Supreme Court for further clarification.

Rapanos v. United States

Perhaps the most important case interpreting the definition of WOTUS is the Supreme Court decision in Rapanos v. U.S., 547 U.S. 715 (2006). In Rapanos, the court considered whether a series of wetlands fell under the jurisdiction of the CWA. Of the wetlands at issue, one emptied into a man-made drain that itself emptied into a creek which eventually emptied into Lake Huron. Another was connected to a drain that shared a surface connection with the Tittabawassee River, and the third wetland shared a surface connection with the Pine River which flows into Lake Huron. At question was whether CWA jurisdiction extended to nonnavigable wetlands that did not abut a navigable water.

Although many hoped that the Supreme Court’s decision in Rapanos would bring clarity to the definition of WOTUS, there was no single, unified standard that came out of the case. While five of the nine justices agreed on the outcome, they did not agree on the legal reasoning behind the outcome. Instead, a four-justice plurality opinion authored by Justice Scalia, and an opinion by Justice Kennedy writing for himself offered two alternative methods for determining whether a water was jurisdictional.

The plurality decision proposed a more strict, black-and-white rule for determining whether a water was a WOTUS. According to the plurality, the word “waters” in “waters of the United States” should be taken to mean only “relatively permanent, standing or continuously flowing bodies of water” such as stream, oceans, rivers, and lakes. This would exclude any waterbody through which water flows only intermittently or ephemerally, and would only include wetlands if the wetland had a “continuous surface connection” to another WOTUS.

The test authored by Justice Kennedy took a different approach. According to Justice Kennedy, the CWA required a more flexible approach. He suggested that the jurisdiction of each water should be determined on a case-by-case basis, and that jurisdiction should be based on whether the water in question has a “significant nexus” to a water that has been used for interstate commerce. For wetlands, a significant nexus would exist if the wetlands “significantly affect the chemical, physical, and biological integrity” of another WOTUS. In that case, the wetland would be considered a WOTUS and would fall under the jurisdiction of the CWA.

After the Supreme Court released its decision in Rapanos, lower courts have struggled to determine which test to apply when analyzing CWA jurisdictional disputes. When the Supreme Court agrees only on the outcome of the case, but not on the legal basis for that outcome, previous Supreme Court rulings have specified that lower courts must follow the judgment which interprets the law in the narrowest manner. However, this has been some dispute over whether the plurality approach, or the Kennedy approach provides a narrower interpretation of the CWA. So far, courts that have addressed the issue have either applied Justice Kennedy’s significant next test either alone or in combination with the plurality’s test. No court has yet to apply the plurality test on its own. For its part, EPA has tended to apply the Kennedy test.

Interpreting Memorandum

Along with lower courts, EPA also had to determine the appropriate way to implement WOTUS following the Rapanos decision. In 2008, EPA and the Corps issued a joint guidance document directing both agencies on how to interpret the definition of WOTUS in light of Rapanos. In that guidance document, EPA and the Corps divided waterbodies into three general categories: (1) waters that the agencies will assert CWA jurisdiction over; (2) waters that the agencies will determine CWA jurisdiction over after determining whether they have a significant nexus with another WOTUS; and (3) waters that the agencies would generally not assert jurisdiction over. Additionally, the memoranda detailed how EPA and the Corps would apply the significant nexus standard.

Of the waters that the agencies would continue to assert CWA jurisdiction over, EPA included traditionally navigable waters, wetlands adjacent to those waters, non-navigable tributaries of traditionally navigable waters that are relatively permanent, and wetlands that directly abut those tributaries. As always, EPA defined traditionally navigable waters as “all waters which are currently used, or were used in the past, or may be susceptible to use in interstate or foreign commerce.” In other words, those waterbodies that could be use to ship goods or otherwise facilitate interstate commerce remained clearly jurisdictional under the CWA. EPA would also continue to assert CWA jurisdiction over wetlands that were “bordering, contiguous, or neighboring” traditionally navigable waters. Such wetlands do not need to have a continuous surface connection with a navigable water. While a continuous surface connection with a navigable water is enough to bring a wetland under CWA jurisdiction, wetlands that are physically separated from jurisdictional waters by man-made barriers, natural river berms, or beach dues would also fall under CWA jurisdiction. So would wetlands that share a scientifically-supported ecological connection with a jurisdictional water. EPA also continued to find that non-navigable waterbodies whose waters flow into a traditionally navigable water either directly or indirectly were clearly jurisdictional, as were the wetlands that shared a continuous surface connection with those non-navigable waters.

Waters identified by the 2008 memorandum as requiring a case-by-case analysis to determine whether the water fell under CWA jurisdiction included non-navigable tributaries that were not relatively permanent, wetlands adjacent to such tributaries, and wetlands that are adjacent to but do not directly abut a non-navigable tributary. According to the memorandum, EPA and the Corps would analyze such waters by assessing “the flow characteristics and functions of the tributary itself, together with the functions performed by any wetlands adjacent to that tributary, to determine whether collectively they have a significant nexus with traditional navigable waters.” In other words, the jurisdiction of these waters would be determined according to their chemical, physical, and biological relationship with traditionally navigable waters. To determine that relationship, the agencies noted that they would evaluate both hydrologic and ecologic factors.

Finally, the memorandum stated that neither EPA or the Corps would assert CWA jurisdiction over the following: swales or erosional features such as gullies or small washes that receive a low or infrequent volume of water; and ditches that were “excavated wholly in and draining only uplands” and that do not have a permanent flow of water. Those waters would typically not be considered WOTUS and therefore would not fall under CWA jurisdiction.


After the decision from the federal district court in Arizona, it appears that the NWPR will no longer be used to determine whether a water is a WOTUS. Instead, EPA and the Corps will revert to the regulatory regime that was in place prior to 2015, which consists of the 1980s regulations and some key memoranda. Under that regime, some waters should be readily identifiable as WOTUS, while others will require additional analysis. Traditionally navigable waters, such as the Mississippi River, will fall under CWA jurisdiction. Additionally, any non-navigable tributaries of navigable waters, and any wetlands that abut those tributaries or share a “significant nexus” with a navigable water will also be jurisdictional. From there it gets less clear. Other waters will require EPA or the Corps to perform an analysis to examine the flow characteristics and functions of the water to determine whether it is a WOTUS.

EPA is in the process of drafting new regulations to replace the pre-2015 regulatory regime. Until that point, unless something changes, EPA and the Corps will likely continue to interpret WOTUS according to the pre-2015 regime.


To read the 1980s WOTUS regulations, click here.

To read the text of Rapanos v. U.S., click here.

To read the 2008 memorandum, click here.

To read the decision from the Arizona district court, click here.

For additional National Agricultural Law Center resources on the CWA, click here.