What Happens When Endangered Species Endanger Each Other?

• Published date: 11 December 2025
• Subject Matter: Environment, Environmental Law
• Law Firm: Duane Morris LLP
• Author: Mr John M. Simpson

The U.S. Court of Appeals for the Ninth Circuit decided an interesting Endangered Species Act (ESA) case this week. San Luis Obispo Coastkeeper v. County of San Luis Obispo, No. 24-7807 (9th Cir. Dec. 3, 2025).

Certain environmental NGO's claimed that San Luis Obispo County's operation of a dam potentially harms the steelhead trout, a fish listed as threatened under the ESA. Plaintiffs sought a mandatory preliminary injunction directing changes in the dam's water flow operation to help the trout. The county opposed, arguing that the mandated operational changes would harm the California red-legged frog and the tidewater goby, both of which live in the same habitat and are listed as endangered under the ESA. The district court granted the injunction without considering the impact on the frog and the goby. The Ninth Circuit reversed.

The appellate court noted that, in ESA cases, only the first two parts of the four-part standard for an injunction - (1)...