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Even before the Supreme Court ruled late last month in Loper Bright Enterprises v. Raimondo, a lawsuit over a herring fishing regulation, Meredith Moore knew the case was never really about fish. Moore, the director of the fish conservation program at the nonprofit environmental group Ocean Conservancy, instead saw the case as a “Trojan horse” that would weaken public agencies’ regulatory power across the board and unleash a wave of lawsuits aimed at unraveling environmental protections. “This is an opportunity for a free-for-all,” she says.

“This is an opportunity for a free-for-all.”

As Moore had feared, when it came time for the Court to deliver its June 28 decision on Loper Bright (which it had merged with a near-identical case, Relentless, Inc. v. Department of Commerce), the conservative majority overturned a decades-old legal precedent known as “Chevron deference.” Named after a 1984 Supreme Court case involving the oil giant, the doctrine was one of the most cited legal precedents ever. For 40 years, it instructed judges to defer to an agency’s interpretation of a law—say, the Clean Water Act, Social Security Act, Affordable Care Act—when that law was unclear. Now, thanks to the pair of lawsuits (and the anti-regulatory interests like Charles Koch, who backed them), the power to determine the “best” reading of ambiguous statutes now falls to judges, not agency officials.

The decision, many legal experts warn, will curtail federal agencies’ ability to regulate everything from tax policy to reproductive rights and the environment, and is likely to be one of the court’s most significant actions in recent history—on par with decisions that overturned the right to abortion and ended affirmative action.

While it’s clear that the decision will be extraordinarily broad (which I’ve written about here and here), the specific, concrete details about its impact are less obvious. What will the ruling mean, for instance, for herring? Or other fish we eat? Or any of the more than 1,000 threatened and endangered species in the US?

Let’s start with herring. The regulation that sparked Relentless and Loper Bright required herring fishermen to pay for boat observers to monitor their catches—around $700 per trip—a........

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