When Congress debated the Endangered Species Act of 1973, bill sponsors expressed concern about individuals who capture or kill animals “for pleasure or profit” and also recognized habitat destruction as a principal threat to protected species. With its core purpose to make it unlawful for any person to “take” a listed species anywhere in the United States (including killing, injuring, capturing, harassing, or “harming” an animal), the Senate’s original bill (S. 1983) would have defined “take” to include “the destruction, modification, or curtailment of [the] habitat or range” of fish or wildlife. The Commerce Committee deleted that language before the bill reached the floor, without explanation. Senator Tunney added it by floor amendment, with no debate on what it meant. Congressional Record, vol. 119, 1973, pp. 25691, 30162.
With little legislative history to go on, significant investment in our water delivery, flood protection, and wildlife management system turns on how the ESA defines “harm” in its definition of “take.” The breadth of that term determines when otherwise lawful operation of existing infrastructure may trigger the ESA’s take prohibition because of its effects on listed species or their habitat. Recent efforts by the current federal administration highlight the difficulty in meeting the United States Supreme Court’s mandate in its landmark 1978 decision Tennessee Valley Authority v. Hill, 437 U.S. 153, to protect species “whatever the cost,” while also allowing ongoing activities that deliver water to farms, homes, and businesses and protect communities from flooding.
In 1995, the United States Supreme Court weighed in. In Babbitt v. Sweet Home Chapter of Communities for a Great Oregon, 515 U.S. 687, small landowners and timber interests challenged the Fish and Wildlife Service’s 1975 regulation defining “harm” as “an act which actually kills or injures wildlife,” including “significant habitat modification or degradation” that kills or injures wildlife by significantly impairing breeding, feeding, or sheltering. Writing for a six-Justice majority, Justice Stevens upheld the regulation as a reasonable interpretation and deferred under previous rules of Chevron deference to the agency interpretation of a statute. Justice O’Connor joined the majority but wrote separately to emphasize the limits imposed by proximate causation. In her view, “harm” applies only where significant habitat modification, by impairing essential behaviors, proximately and foreseeably causes actual death or injury to identifiable, individual protected animals. Justice O’Connor illustrated the line with two examples. A landowner who drains a pond on his property and kills the endangered fish in it would satisfy any test of proximate cause. A farmer whose fertilizer is picked up by a tornado and dropped miles away in a wildlife refuge would not. Justice Scalia, joined by Chief Justice Rehnquist and Justice Thomas, dissented. He read “take” as a centuries-old term of art for reducing wild animals to human control by killing or capturing them. On that reading, it covers only affirmative acts, not omissions, done directly and intentionally to particular animals, not to populations. Under Justice Scalia’s interpretation, poisoning an animal or cutting down its nest tree would qualify, but routine farming, ranching, or logging that incidentally injures wildlife would not.
Thirty-one years after Sweet Home, the federal wildlife agencies adopted the dissent. The Fish and Wildlife Service (“USFWS”) and the National Marine Fisheries Service (“NMFS”) proposed rescinding their regulatory definitions of “harm” in April 2025, received roughly 358,000 comments, and published the final rule on July 14, 2026. The rule deletes the definition of “harm” and adopts no replacement. The Services’ rationale is that Loper Bright Enterprises v. Raimondo (2024) 603 U.S. 369 ended Chevron deference and requires the “single, best meaning” of the statute. Under Loper Bright, judges now decide for themselves what a statute means, and the agencies argue that the old “harm” rule cannot survive that test. Going forward, the Services expressly adopt Justice Scalia’s reading: “take,” including “harm,” reaches only affirmative acts directed immediately and intentionally at a particular animal, not acts that indirectly and accidentally injure a population. The rule is already in litigation. Challengers argue that under Loper Bright, courts, not agencies, decide the best reading, and that the Services cannot adopt a reading the Supreme Court rejected in Sweet Home. State of California v. Burgum (N.D.Cal., No. 3:26-cv-10071, complaint filed Sept. 9, 2026); Swinomish Indian Tribal Community v. National Marine Fisheries Service (W.D.Wash., No. 2:26-cv-02473, complaint filed July 14, 2026).
Both USFWS and NMFS recently issued internal guidance applying Justice Scalia’s interpretation beyond habitat modification to the ESA’s broader prohibition on “take.” In separate memoranda, FWS Director Brian Nesvik and NOAA General Counsel John Luce instructed agency staff that “take” reaches only an affirmative act intentionally and purposefully directed at a particular animal, and that the relevant intent concerns acting on the animal itself rather than merely intending to engage in the underlying activity. Both memoranda offer two examples. A vessel that inadvertently strikes a whale has not taken it because its course was not set against the whale. Felling a tree is not a take of bats roosting in it unless the tree is cut to kill or capture them. Read literally, this would place most incidental deaths from development, transportation, logging, and water operations outside of the ESA’s prohibition on take.
However, this reading of “intent” goes against the approach the Supreme Court’s majority adopted in Sweet Home, which rejected the idea that “harm” applies only when a person specifically intends to injure protected wildlife. On October 1, nine environmental groups represented by Earthjustice expanded their existing lawsuit to challenge the new agency memoranda.
For consumers and users of water in California, the practical question is whether changes to the ESA’s definition of harm will lead to improved conditions for species without unreasonably interfering with day-to-day water needs. The ESA’s separate mandate to avoid jeopardizing listed species will remain the standard for federal water projects such as the Central Valley Project through the Section 7 consultation process. What may change is just how far those operations must go to avoid harm to protected species. Short of intentional harmful activity, the question remains how to balance the water needs of all water users and whether, instead of avoiding harm, we should instead focus on alternative ways to utilize water to provide benefits and necessary protections for protected species.
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