In a precedential decision, the Ninth Circuit recently modified its approach to mandatory injunctive relief in Endangered Species Act (ESA) cases involving multiple species.  The court, in San Luis Obispo Coastkeeper et al. v. County of San Luis Obispo, No. 24-7807 (9th Cir. Dec. 3, 2025), held that “when mandatory injunctive relief under the ESA may benefit one protected species at the expense of other protected species, a court must consider competing equities and the public interest as to those other species.”

The case involved a challenge to the County of San Luis Obispo’s management of the Lopez Dam and Reservoir, located on the Arroyo Grande Creek in California, which flows into the Pacific Ocean.  Several environmental groups filed suit against the County, contending that the dam interfered with the migratory and reproductive life cycle of the steelhead trout, a threatened species under the ESA.  The environmental plaintiffs sought a mandatory preliminary injunction – “mandatory” because it would require the County to take affirmative action rather than to refrain from acting – obligating the County to develop a plan to increase the release of water flows from the dam, as well as other actions.

Before the district court, the County argued that the plaintiffs’ requested relief would harm two other ESA-listed species: the California red-legged frog and the tidewater goby.  The district court nevertheless issued a preliminary injunction order that contained most of the environmental groups’ requested relief.  The County then appealed.

The court of appeals, in an opinion authored by Judge Nguyen, began by recognizing that the Ninth Circuit has for decades treated requests for preliminary injunctions under the ESA differently than requests made under other statutes.  Under the standard approach to injunctive relief, the court applies a “familiar four-factor test,” whereby “[a] party is entitled to a preliminary injunction if it demonstrates ‘(1) that it is likely to succeed on the merits, (2) that it is likely to suffer irreparable harm in the absence of preliminary relief, (3) that the balance of equities tips in its favor, and (4) that an injunction is in the public interest.’”  Slip op. at 16 (quoting Flathead-Lolo-Bitterroot Citizen Task Force v. Montana, 98 F.4th 1180, 1190 (9th Cir. 2024)).  But in cases under the ESA, the Ninth Circuit generally does not consider the third and fourth factors of this test, reasoning that Congress in the ESA already has struck the balance of equities in favor of protected species.

Here, however, the presence of the California red-legged frog and the tidewater goby – in addition to the steelhead trout, which the plaintiffs sought to protect – “test[ed] the logic” of the Ninth Circuit’s existing approach.  The court explained that when a request for injunctive relief pits the interests of one protected species against those of others, “[t]he ESA’s command to prioritize endangered species becomes a one-way ratchet, favoring one listed species without any room to weigh the cost to another.”  Slip. op. at 20.  Accordingly, in circumstances such as these, the district court “must balance the equities and consider the public interest as to the other listed species.”  Because the district court did not do so here, the court of appeals vacated the preliminary injunction and remanded the case for further proceedings.

The court rejected, however, the County’s effort to broaden the district court’s equitable discretion.  The County argued that once the door had been opened to equitable balancing, then the district court “must consider all equities and all interests—not just those of the protected species,” including economic and resource-management factors.  Slip op. at 15, 20-21.  But the court explained that its holding was based on the concern that “[w]ithout equitable discretion, a court could end up ordering relief that saves one species at the expense of another.”  Id. at 20.  The Ninth Circuit still recognizes that, in the ESA, “Congress was clear that endangered species come first, ‘whatever the cost.’”  Id. at 21 (quoting Tenn. Valley Auth. v. Hill, 437 U.S. 153, 184 (1978)).

Finally, the court stressed that its decision “does not require a district court to deny relief whenever another species might be affected,” as, “[i]f courts had to reject an injunction every time a defendant could point to another at-risk species, the ESA’s protections would become hollow in these circumstances.”  Id.  Rather, a district court must weigh the equities and determine whether injunctive relief is warranted, and, if so, what that relief should be.

Judge VanDyke, while joining the majority’s opinion, also wrote separately to emphasize that mandatory injunctions are “disfavored” and that, in circumstances such as those presented by this case – involving the complex interplay of multiple protected species sharing a habitat – “proving that ‘the facts and law clearly favor’ the party requesting a mandatory preliminary injunction is a difficult endeavor—as it should be.”  Id. at 26-27.

The Ninth Circuit’s decision in San Luis Obispo Coastkeeper illustrates both the force of the ESA as well as the value of looking beyond a litigant’s focus on a particular species, given that a mandatory injunction aimed at helping one species may have negative effects on another.

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