What, exactly, is a wetland?

Careful — the answer could result in a lot fewer of them.

This fall the U.S. Supreme Court will hear a case that could gut federal oversight of the nation’s fragile wetlands and the critical role they play in clean water.

Plaintiffs in the case, Sackett v. Environmental Protection Agency, are effectively asking the court for a narrow definition of “Waters of the United States,” limiting federal regulatory authority.

For years, the prevailing legal view has been that this authority should be fairly broad. But then along came Chantell and Michael Sackett.

The Idaho couple wanted to build a house on a lot containing wetlands. They got the requisite local permits, but then were informed by the EPA that their wetlands qualified as regulated waters, meaning they needed a costly federal permit before building.

The EPA relied on an interpretation of the federal Clean Water Act which held that any water with a “significant nexus” to a navigable waterway — any surface, chemical or biological connection — fell under federal jurisdiction.

But in fact, the courts have never come to a clear conclusion on how to define federal jurisdiction. In a landmark 2011 case, U.S. Supreme Court Justice Antonin Scalia proposed a different definition — to receive federal protection, waters must be “relatively permanent” and have a “continuous surface connection” to navigable waters.

The Sacketts argue the Scalia definition should prevail. If it does, legal experts say it could dramatically reduce federal authority over wetlands and possibly other waters — which in turn could reduce the benefits they provide, leading to dirtier water.

In an amicus brief filed by 12 national and international scientific societies, scientists and their attorneys argue that if the court adopts the Sacketts’ preferred definition, “more than 50% percent of wetlands in some watersheds would no longer be protected by the Clean Water Act.”

If applied to streams, the scientists say, “ephemeral and intermittent streams would not be jurisdictional waters, and thus more than 90% percent of stream length in some watersheds would no longer be protected by the Clean Water Act.”

Attorneys representing the scientists include Royal Gardner, a law professor at Stetson University and member of the Policy & Science Committee for Friends of the Everglades, VoteWater’s 501(c)3 sister organization.

Sound science, they argue, is crucial if the Clean Water Act is to actually ensure clean water.

“Wetlands and streams contribute significantly to the chemical, physical, and biological integrity of traditional navigable waters,” they write in the brief. They retain and store sediments, contaminants and stormwater; they “act as refuges and provide protection and habitat for fish, shellfish, and wildlife.”

If the court rules for the Sacketts, regulatory authority would fall to individual states. But as E&E News Greenwire reported earlier this year, “some states may have their own rules to protect wetlands and waterways no longer covered by the Clean water Act, (but) many do not. Some state regulators have even been prohibited by their legislatures from enforcing standards stricter than the federal government’s.”

In other words, if federal protections are dropped — how well will the states protect these fragile waters? Will understaffed and underfunded state regulatory agencies have the capacity to take on this new task? Might state legislatures, en thrall to special interests, chip away at local protections, ultimately resulting in more pavement and fewer swamps, marshes and bogs?

Such a result, write the scientists in their amicus brief, “would be contrary to the only objective that Congress identified in the Clean Water Act: restoring and maintaining the integrity of the Nation’s waters.”

It’s an objective that must be preserved.