• The Ninth Circuit held in Inland Empire Waterkeeper v. Corona Clay Co. that whether a waterbody qualifies as a “water of the United States” is a merits question rather than a threshold jurisdictional issue — even though “waters of the United States” is what sets the Clean Water Act’s jurisdiction.
• Meanwhile, the EPA and Army Corps of Engineers supplemented their proposed rule that would further narrow “waters of the United States” to certain perennial waterbodies rather than to waters meeting a “wet season” test, as was proposed in September 2026.
• These developments underscore the ongoing challenges of understanding and complying with the Clean Water Act’s reach.

It remains a struggle to keep pace with ongoing changes to the lynchpin of the Clean Water Act’s jurisdiction: how we define “waters of the United States.” Several presidential administrations have tried defining, and redefining, this jurisdictional reach.

These changes were the focus of an appeal in Inland Empire Waterkeeper v. Corona Clay Co., in which a clay-recycling facility was sued under the Clean Water Act. A trial court found the facility liable for discharging pollutants into Temescal Creek. After the trial, however, the Supreme Court decided Sackett v. EPA, which narrowed the Clean Water Act’s jurisdictional reach by interpreting “waters of the United States” to cover “relatively permanent, standing or continuously flowing” water bodies. Seizing on Sackett, the facility moved to dismiss the case for lacking jurisdiction because Temescal Creek was no longer a “water of the United States” under this new standard. The court had no power to hear the case, so the facility argued.

The Ninth Circuit rejected the argument. In its opinion from September 3, the court held that the Clean Water Act’s citizen-suit provision confers jurisdiction over alleged violations, even if the facility may later disprove whether the facility discharged into a jurisdictional “water of the United States.” That conclusion may seem somewhat paradoxical as defining “waters of the United States” is a jurisdictional issue. But as the Ninth Circuit put it, “whether a case brought under the Clean Water Act involves a water of the United States is a merits question, not a question of jurisdiction.” On remand, the district court must resolve the factual issue of whether Temescal Creek is a jurisdictional “water of the United States.”

Meanwhile, the Environmental Protection Agency and Army Corps of Engineers added some complexity by re-defining, again, “waters of the United States.” As we previously covered, the EPA and Army Corps proposed redefining “waters of the United States” in November 2025 by tying it to “relatively permanent” (the phrase the Supreme Court used in Sackett) and further defining that phrase to include a “wet season” test. After receiving about 220,000 public comments, the agencies issued a “supplemental notice of proposed rulemaking” in September 2026 that makes a few changes. Among those changes is a proposal to remove the “wet season” test. In its place, the agencies now try defining “relatively permanent” to mean perennial bodies of water. A perennial body of water must have standing or continuously flowing water. A perennial body would not lose its status, the supplemental notice explains, even if a non-anomalous event interrupts flow for a single period of up to 30 consecutive days in a given year. But the water body would become ephemeral and non-jurisdictional if flow is interrupted for more than a single period in any given year and the interruptions are non-anomalous and ordinary for that water body. By example, if a non-anomalous event interrupts flow twice in a year for at least 10 consecutive days of no flow for each period, then the water body is considered non-jurisdictional. 

The EPA and Army Corps began this rulemaking process with an aim at simplifying how the Clean Water Act applies so that its definition would be “durable.” Time will tell whether these changes can achieve that goal. But as Inland Empire Waterkeeper v. Corona Clay Co. reminds us, project proponents must stay apprised of these changes regardless.

The EPA and Army Corps are accepting public comments on the supplemental notice of proposed rulemaking for 30 days once it is published in the Federal Register. Please contact Hanson Bridgett’s Environmental & Water Law attorneys if you have questions about engaging in the rulemaking process or understanding how changes in the Clean Water Act could affect land development and permitting in California.