Ephemeral streams in Chinle Valley, ArizonaMarli Miller/Getty

Last year, in one of the most significant environmental legal cases in recent history, the Supreme Court’s conservative majority severely limited the federal government’s ability to regulate waterways. By narrowly interpreting the Clean Water Act as only applying to “relatively permanent, standing, or continuously flowing bodies of water” and wetlands with a continuous surface connection to those bodies, the court effectively cut federal protections for more than half of the country’s wetlands. Around 90 million acres of marshy areas are now much more vulnerable to pollution.

Scientists knew immediately the consequences of the case, Sackett v. EPA, would be massive—one plant biologist I spoke to last year who’d devoted her retirement to protecting wild Venus flytraps called it “the worst thing that’s happened in my conservation life.” But determining how the decision would impact the country’s vast network of rivers, lakes, and streams would take time and some scientific digging.

More than half of the water in the US’ major rivers originates from ephemeral streams.

Now, a year later, some of that research is trickling in: A new study from researchers at Yale and the University of Massachusetts, Amherst, published in Science last week, reveals why removing federal protections for some non-permanent waters could have a huge effect on the nation’s rivers.

The study focused on short-lived streams, fueled by rain or snow, called “ephemeral streams,” which the Sackett decision now excludes from federal protection under the Act. When an ephemeral stream is not flowing with rainwater, lead author and recent Yale postdoc Craig Brinkerhoff explains, it may look something like a dry........

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