About 55 percent of the water emanating from U.S. rivers is vulnerable to pollution, due to their lack of protections under the Clean Water Act, a new study has found.
The Supreme Court last year ruled that “ephemeral streams” — those that fill up and flow only after weather events — do not fall under the jurisdiction of the Clean Water Act, the authors noted.
Yet these fleeting entities furnish about 55 percent of the water that empties out of regional river systems across the country, according to the study, published Thursday in Science.
Within that national figure, the study also identified a stark regional divide: Rivers west of the Mississippi River are far more influenced by ephemeral resources than those on the other side.
For example, about 94 percent of the water pouring out of river systems in Nevada’s Black Rock Desert and in California’s Humboldt County come from temporary stream sources, per the study.
“The irony is that the federal Clean Water Act was adopted precisely because state and local governments were thought to be doing a poor job of protecting the nation’s waterways,” co-author Doug Kysar, a professor at Yale Law School, said in a statement.
“States don’t necessarily have incentives to adopt costly water protections when the benefits will be felt by ecosystems out of state,” Kysar added.
Nonetheless, the Supreme Court in May 2023 determined the only entities protected are “those relatively permanent, standing or continuously flowing bodies of water.” These bodies, per the decision, form “geographical features that are described in ordinary parlance as streams, oceans, rivers, and lakes.”
In response, the Environmental Protection Agency then narrowed the scope of its Waters of the United States rule — determining that wetlands would only be protected if they have a clearer connection to permanent waterways.
Regardless of the recent downgrades in federal oversight of waterways, Kysar emphasized that contamination is a transboundary concern that affects interstate commerce.
The new study, he noted, demonstrates “just how far downstream from an ephemeral waterway the ultimate impacts of pollution can be felt.” He therefore stressed the importance of regulating temporary streams even if they don’t meet historic definitions of navigable waters.
To back up this perspective, the scientists developed a model to quantify ephemeral stream contributions to more than 20.7 million permanent water bodies in the contiguous U.S.
They found that temporary waters flow less frequently in the U.S. West — about four to 46 days each year — compared to the East Coast, where they flow 173 days on average annually.
Yet despite their relatively infrequent occurrence in the U.S. West, ephemeral streams in this region are responsible for as much as 79 percent of downstream river flow. Their Eastern counterparts, on the other hand, are responsible for only about 50 percent on average, according to the study.
While ephemeral streams are fleeting by nature, a big rain event can mean that “all of a sudden you’re pushing the stuff that’s been accumulating in those rivers downstream,” lead author Craig Brinkerhoff, a recent PhD recipient from the University of Massachusetts Amherst.
“In theory, pollution in those ephemeral streams will ultimately influence water many kilometers away that is, at least nominally, still regulated by the Clean Water Act,” he added.
Although the ephemeral stream flow might have greater impacts on U.S. West rivers, Brinkerhoff noted that even humid East Coast areas with copious groundwater supplies are affected by these fleeting resources.
Colin Gleason, a University of Massachusetts Amherst professor of civil and environmental engineering, looked to his own watershed, the Connecticut River, as an example.
He stressed that while the Connecticut River has rules governing which pollutants can be released into the waterway, dumping that occurs in dry gullies uphill can end up in the river’s main stem.
“On a day in which every stream in the Connecticut River is flowing with its average annual condition, 59 percent of the water entering Long Island Sound was sourced from these ephemeral streams,” Gleason said.
Around the country, the researchers found that “ephemeral connectivity is a substantial pathway” for the transport of both water and pollutants — one that has the potential to influence the quality of this quintessential resource.
“Our study provides more concrete evidence that all of these things are connected,” Brinkerhoff added. “We can’t regulate water bodies ad hoc.”