Clean Water Act Leaves about 55% of Water Flowing Out of Rivers Vulnerable to Pollution, New Study Suggests

"The Clean Water Act regulates where and how much we can dump into water bodies-water bodies being rivers, lakes, wetlands, reservoirs, etc.," says Brinkerhoff. And the implications of this new research for water pollution are clear: "[Ephemeral streams are] not flowing most of the time, but then you get a big enough rainstorm and all of a sudden you're pushing the stuff that's been accumulating in those rivers downstream. 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 says.

Doug Kysar, Joseph M. Field '55 Professor of Law at Yale Law School, and one of the study's authors, says that this work helps provide a constitutional basis to include ephemeral streams in the CWA. "Water pollution is a transboundary issue that clearly implicates interstate commerce, such that Congress could regulate ephemeral streams even if they are not the kind of 'navigable waters' that Congress has historically exerted federal authority over."

However, he also says that it's more likely that this responsibility will fall to state and local governments. "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," he adds. "Our research helps to explain why that would be the case, as it shows just how far downstream from an ephemeral waterway the ultimate impacts of pollution can be felt. States don't necessarily have incentives to adopt costly water protections when the benefits will be felt by ecosystems out of state."

One thing the researchers emphasize is that the size of the river basin used for their modeling does influence the results. The 55% figure is only true when you divide river basins into a certain size-if they had used smaller basins, the ephemeral influence would be larger, and if they used bigger basins, the influence would be less. But even using the scale they did-which is the second-largest river basin scale defined by the U.S. Geological Survey-ephemeral streams still influenced more than half of rivers' total water output. In other words, 55% is a quite surprising finding for rivers so large, the researchers say. Previous thinking was that ephemeral streams only influence their immediate areas.

"Our study provides more concrete evidence that all of these things are connected," says Brinkerhoff. "We can't regulate water bodies ad hoc."