On March 30, 2026, a federal court in California issued a ruling to overturn several Endangered Species Act (“ESA”) regulations adopted by the Trump administration in 2019 and the Biden administration in 2024. The plaintiffs in Ctr. for Biological Diversity v. U.S. Dep’t of Interior, No. 24-cv-04651 (N.D. Cal. Mar. 30, 2026) challenged six rules in total with the court ultimately concluding that four violated the statutory text of the ESA. Earlier this year, the United States Fish and Wildlife Service (“FWS”) together with the National Marine Fisheries Service (“NMFS”) proposed a slate of new ESA regulations intended to restore the rules established under the first Trump administration. While those rules have yet to be finalized, it is possible that the recent court ruling may offer some insight into how courts may ultimately treat those regulations.
ESA Overview
The ESA was enacted in 1973 for the purpose of conserving species at risk of extinction and the habitats upon which those species depend. 16 U.S.C. § 1531(b). The statute is jointly administered by FWS and NMFS (collectively, “the Services”) which are responsible for creating and maintaining a list of species that are classified as either “threatened” or “endangered” depending on the level of risk those species face. 16 U.S.C. § 1533. Once a species is added to that list, it becomes protected under the ESA.
When the Services list a species for protection under the ESA, they must also designate critical habitat for the species. 16 U.S.C. § 1533(a)(3)(A)(i). The ESA defines critical habitat as specific geographical areas which are “occupied by the species, at the time it is listed […] on which are found those physical or biological features essential to the conservation of the species” or areas which are not occupied by the species at the time of listing but the Services have determined are “essential for the conservation of the species.” 16 U.S.C. § 1532 (5)(A).
Along with requiring the Services to list species under the ESA and designate critical habitat for those species, the ESA also requires all other federal agencies to consult with the Services to avoid harming listed species or designated critical habitat. Specifically, the ESA requires each federal agency to ensure that any action it “authorize[s], fund[s], or carrie[s] out” is “not likely to jeopardize the continued existence of any [listed] species or result in the destruction or adverse modification of” critical habitat. 16 U.S.C. § 1536(a)(2). To initiate this process, the agency taking action will determine whether its action “may affect” listed species. 50 C.F.R. § 402.13. If the agency concludes that its action “may affect” a listed species, it must reach out to the Services to determine whether the action is “likely to adversely affect” the species. 50 C.F.R. § 402.13 If so, then the Services must engage in formal consultation, a process which requires the consulting Service to prepare a document known as a Biological Opinion (“BiOp”). 50 C.F.R. § 402.13 The BiOp will evaluate more thoroughly the expected impacts of the agency’s action and if it concludes that the action is likely to jeopardize the continued existence of a protected species or result in the destruction or adverse modification of critical habitat, it must also include mitigation measures the agency can take to avoid causing such negative impacts. 50 C.F.R. § 402.13. When making a determination about the impacts an agency action may have on listed species, the Services must base their conclusions on “the best scientific and commercial data available.” 16 U.S.C. § 1536(a)(2).
Background to the Case
Since 2019, the ESA has experienced several rounds of regulatory changes. In August 2019, the Services issued final rules to change the procedures related to the listing of species under the ESA and the consultation process between the Services and other federal agencies. A closer look at those changes is available here. The plaintiffs in Ctr. for Biological Diversity v. U.S. Dep’t of Interior filed a lawsuit to challenge those 2019 regulations. However, following a change in Presidential administration, the court sent the matter back to the Services for review, bringing that lawsuit to an end. In 2024, the Services adopted new regulations which, according to the plaintiffs, resolved some of their concerns with the 2019 regulations but ultimately retained certain issues while introducing others. More information on the 2024 regulatory changes can be found here.
After the new regulations were finalized in 2024, the plaintiffs filed the current lawsuit to challenge six specific provisions that had been either introduced in 2019 and retained in 2024 or introduced for the first time in 2024. Following another change in Presidential administration in 2025, the Services sought to have the case either paused or dismissed, citing another round of updated ESA regulations that had been proposed in 2025 which the Services expect to finalize before the end of 2026. However, the court concluded that neither pausing or dismissing the case would be appropriate, noting that it would be better for the court to “provide the [Services] with its reading” before the new regulations are final so that the Services can take into account any “problems” the court might find.
Many of the regulatory changes proposed in 2025 were identical to those that had been made in 2019 before being modified in 2024. Although various lawsuits were filed to challenge the 2019 rules, they were largely paused or dismissed after the Services announced that they would revisit those regulations following the transition from the Trump administration to the Biden administration. For that reason, no court ever fully considered whether the 2019 rules complied with the ESA. The recent decision in Ctr. for Biological Diversity v. U.S. Dep’t of Interior represents the first time a court has considered the legality of those regulations and may provide some insight into how the rules proposed in 2025 may be viewed by courts after they are finalized.
Recent Court Decision
The plaintiffs in Ctr. for Biological Diversity v. U.S. Dep’t of Interior asked the court to review six ESA regulations and consider whether they violated the statutory requirements of the ESA. Four of those regulations are related to the consultation process while the other two are concerned with the designation of critical habitat. Of those six, the court found that four violated the ESA and should be overturned. The other two were upheld.
“Effects of the Action”
During agency consultation with the Services, the ESA requires the Services to evaluate the effects of the agency action on listed species and critical habitat to determine whether jeopardy of a species or the destruction or adverse modification of critical habitat is likely to occur. 16 U.S.C. § 1536. Before 2019, the ESA regulations defined “effects of the action” as “the direct and indirect effects of an action on the species or critical habitat.” 50 C.F.R. § 402.02 (2018). The 2019 rules changed the definition of “effects of the action” to “all consequences to listed species or critical habitat that are caused by the proposed action” and clarified that a “consequence is caused by the proposed action if it would not occur but for the proposed action and it is reasonably certain to occur.” 50 C.F.R. § 402.02 (2019). The Services left this definition in place when it amended the regulations in 2024.
The plaintiffs argue that this violates the ESA’s requirement that the Services rely on the best scientific data available when considering the impacts an agency’s action may have on listed species and that it the phrase “reasonably certain to occur” conflicts with the ESA requirement that the Services consider whether jeopardy of a species is “likely” to occur. The court agreed with the plaintiffs on both arguments. First, the court concluded that the 2019 rule violates the ESA’s “best available data” requirement because the ESA “imposes a mandatory duty on the Services to analyze the likelihood of jeopardy or harm to habitat using the best available data.” According to the court, the best scientific data available may not be the same as impacts that are “reasonably certain to occur.” Next, the court concluded that the provision of the 2019 regulation that requires the Services to only consider those impacts to species and habitat which are “reasonably certain to occur” is contrary to the ESA requirement that Services consider whether jeopardy of a species or harm to habitat is “likely.” Because what is “likely” may not necessarily include what is “reasonably certain to occur,” the court held that this regulation violated the ESA and should be overturned.
Consideration of Mitigation Measures
When drafting a BiOp, the ESA regulations require the Services to take into account “any beneficial actions” taken or proposed to be taken by the action agency. 50 C.F.R. § 402.14(g)(8). The purpose of this rule is to ensure that the Services consider any activities that are beneficial to listed species that the consulting agency plans to include as part of its proposed action when determining what the impacts of that action could be to protected wildlife. In 2019, the Services amended the ESA rules to clarify that the Services should take such beneficial activities into consideration without “any additional demonstration of binding plans.” 50 C.F.R. § 402.14(g)(8). In other words, the 2019 rules require the Services to give proposed beneficial activities the same consideration as any other portion of the agency action even if the agency has not committed to carrying out those activities.
The plaintiffs argued that this violates the ESA’s requirement that the Services “insure” against jeopardy of listed species by “forcing them to consider amorphous, non-binding mitigation plans in making no-jeopardy findings.” In it’s opinion, the court agreed with the plaintiffs, concluding that the 2019 rule violated the ESA because it does not satisfy the statutory requirement that the Services “insure” against harm to species or habitat. According to the court, the ESA requires beneficial activities to be excluded from consideration unless they are binding.
Definition of “Destruction or Adverse Modification”
Under the ESA, the Services must “insure” that federal agency actions will not cause jeopardy to listed species or “destruction or adverse modification” to designated critical habitat. 16 U.S.C. § 1536(a)(2). Prior to 2019, the ESA regulations defined “destruction or adverse modification” as “a direct or indirect alteration that appreciably diminishes the value of critical habitat for the conservation of a listed species.” 50 C.F.R. § 402.02 (2018). In 2019, that definition was amended to “a direct or indirect alteration that appreciably diminishes the value of critical habitat as a whole for the conservation of a listed species.” 50 C.F.R. § 402.02 (2019). That definition was retained in the 2024 regulations.
The plaintiffs argue that introducing the language “as a whole” violates the ESA by replacing the statutory requirement to avoid all destruction or adverse modification of critical habitat with a regulatory provision that allows at least some destruction or adverse modification of critical habitat. The court agreed, concluding that the text of the ESA “prohibits adverse modification entirely” and that the 2019 rule violated that requirement by permitting at least some adverse modification to critical habitat.
Duty to Request Reinitiation of Consultation
Before 2024, the ESA regulations concerning agency consultation required both the agency taking action or the consulting Service to request reinitiation of consultation under certain circumstances. 50 C.F.R. § 402.16(a) (2023). In 2024, the Services amended their regulations so that only the agency taking action is required to request reinitiation of consultation. The plaintiffs claim that the Services unlawfully rescinded their duty to request reinitiation of consultation, arguing that the Services failed to provide adequate reasons to support amending the regulations. In 2024, the Services stated that they were amending the regulation to clarify that only the action agency has the authority and responsibility to initiate or reinitiation consultation. The court was not persuaded by that reasoning. According to the court, while the text of the ESA does not allow the Services to compel any federal agency to engage in consultation, nothing in the pre-2024 rule gave the Services that authority. The rule required the Services to request reinitiation in certain circumstances but did not grant the Services the authority to require the federal agency to reinitiate consultation. Because the Services failed to provide a persuasive reason for changing a rule that had been in place for 25 years, the court found the change to be unlawfully arbitrary and concluded that it should be overturned.
Rules Upheld
Finally, the court considered the last two regulations challenged by the plaintiffs. While the court overturned the first four regulations it considered, it upheld the last two after concluding that they did not violate the ESA.
The ESA defines “threated species” as “any species which is likely to become an endangered species within the foreseeable future[.]” 16 U.S.C. § 1532(20). Before 2024, the ESA regulations required the Services to defined “foreseeable future” as extending “only so far into the future as the Services can reasonably determine that both the future threats and the species’ responses to those threats are likely.” 50 C.F.R. § 424.11(d) (2023). In 2024, the Services amended that definition to “as far into the future as the Services can make reasonably reliable predictions about the threats to the species and the species’ responses to those threats.” 50 C.F.R. § 424.11(d) (2025). In making this change, the Services replaced language requiring that they “reasonably determine” that threats to a species are “likely” with language that the Services make “reasonably reliable predictions” about those same threats. The plaintiffs argued that the new language contradicts the ESA requirement that the Services base their conclusions on the “best available data,” but the court disagreed. In its ruling, the court concluded that the two phrases “appear synonymous” and that to determine whether an effect is “likely” requires making a “reliable prediction” about that effect. Because the court determined that the pre-2024 rule and the amended rule are functionally equivalent, it concluded that the rule should be upheld.
Finally, the court considered the plaintiffs’ challenge to an ESA regulation concerning the designation of critical habitat. The text of the ESA requires the Services to designate critical habitat at the same time it lists a species “to the maximum extent prudent and determinable.” 16 U.S.C. § 1533(a)(3). Before 2024, the ESA regulations identified two limited circumstances where designating critical habitat at the same time a species is listed would not be prudent and determinable. In 2024, the Services modified the regulation to include two other circumstances where designating critical habitat would not be necessary. The plaintiffs argue that the new rule violates the ESA by unlawfully expanding the conditions under which the Services may find that designating critical habitat is not prudent and determinable. However, the court disagreed, citing previous court decisions which held that the Services could only make a not-prudent finding with respect to critical habitat would be beneficial to the species. Because the two additional circumstances outlined in the 2024 ruling described situations where reaching a not-prudent finding would be beneficial to the species, the court found that the regulation complied with the ESA and should be upheld.
Going Forward
Since 2019, the ESA has seen several rounds of regulatory updates. So far, this is the first time a court has reviewed any of the updated rules on the merits to consider whether they comply with the statutory requirements of the ESA. In 2025, the Services launched a new round of regulatory changes, many of which mirror the changes made in 2019. While those rules have yet to be finalized, the ruling in Ctr. for Biological Diversity v. U.S. Dep’t of Interior may offer some insight into how courts will treat those regulations once they are final. For those who are regulated under the ESA, remaining informed on regulatory changes is helpful to understand how the law will be implemented going forward.
To view the court’s decision in Ctr. for Biological Diversity v. U.S. Dep’t of Interior, click here.
To view the text of the ESA, click here.
For more NALC resources on the ESA, click here.