An Idaho couple’s legal struggle to build a house has convinced the U.S. Supreme Court to pare back the Clean Water Act’s regulatory reach over wetlands.

The nation’s highest court has adopted a stricter limit on which wetlands come under the law’s jurisdiction, setting sharper parameters for the Clean Water Act’s enforcement nationwide.

“Wetlands that are separate from navigable waterways cannot be considered part of those waters, even if they are located nearby,” according to the majority opinion, written by Associate Justice Samuel Alito.

Five justices joined in the opinion and the remaining four concurred in the judgment, meaning they agree with its effect.

Under the majority opinion, the Clean Water Act’s authority extends only to wetlands that are “indistinguishable” from waters of the U.S., such as rivers or lakes.

To establish jurisdiction, federal regulators must establish “the wetland has a continuous surface connection with that water, making it difficult to determine where the ‘water’ ends and the ‘wetland’ begins,” the ruling said.

This new standard supersedes the more expansive test established in a 2006 legal precedent, under which those with a “significant nexus” to navigable waters were regulated.

The U.S. Environmental Protection Agency believed this definition applied to adjacent wetlands, even if separated by land from traditional waters of the U.S., but the majority opinion said “this interpretation is inconsistent with the text and structure of the CWA.”

The EPA’s understanding of the law allows the agency to regulate “truly staggering” territory, but Congress said state governments still have the primary jurisdiction over land and water use, the ruling said. “An overly broad interpretation of the CWA’s reach would impinge on this authority.”

In light of the statute’s criminal penalties, the EPA’s interpretation raises “serious vagueness concerns” because ordinary people should clearly understand what conduct is prohibited without worrying about arbitrary enforcement, the ruling said.

The nation’s highest court must be careful not to go beyond the intent of Congress when “a penal statute could sweep so broadly as to render criminal a host of what might otherwise be considered ordinary activities,” the ruling said.

The dispute over the statute’s scope stretches back decades and has continued despite three earlier Supreme Court decisions.

However, the underlying dispute that led to the most recent ruling began in 2007, when Michael and Chantell Sackett tried building a home on less than an acre of property near Priest Lake, Idaho, that federal regulators claimed was a wetland.

The U.S. Environmental Protection Agency issued a “compliance order” halting construction and requiring fill material to be removed from the site, which the couple wanted to challenge in federal court.

However, the 9th U.S. Circuit Court of Appeals ruled the Sacketts couldn’t initiate the litigation at that point but could obtain judicial review once EPA filed an enforcement action — risking up to $75,000 in civil penalties per day of violation if they lost.

The Supreme Court originally sided with the Sacketts in 2012, ruling that such compliance orders are final agency actions that are subject to landowner lawsuits. The decision allowed the couple to proceed with their complaint, which again ended up before the nation’s highest court a decade later.

In its most recent ruling, the Supreme Court has again reversed the 9th Circuit’s opinion in the case, finding the appellate court wrongly concluded the Idaho property contained wetlands that fall under the Clean Water Act’s jurisdiction.

“The wetlands on the Sacketts’ property are distinguishable from any possibly covered waters,” the ruling said.

The Sacketts claimed their property was separated by a paved road from wetlands that drained into Priest Lake, making it impossible to discharge pollutants into regulated “waters of the U.S.” in violation of the Clean Water Act.

Since no surface or subsurface water flowed from their property to a navigable waterway, the couple argued their lot wasn’t subject to the EPA’s regulatory power under that statute.

They further urged the Supreme Court to abandon the “significant nexus” test, under which the 9th Circuit allowed their property to be regulated because it could affect physical, chemical or biological integrity of a navigable water.

The Sacketts were joined by the American Farm Bureau Federation and 13 other national agriculture groups in arguing the “significant nexus” test was too vague and imposed practically no constraint on federal Clean Water Act authority.

The farm organizations worried the “significant nexus” standard could be interpreted so broadly as to apply to ephemeral drainages and low spots in fields that are rarely wet.

Clean Water Act jurisdiction can reduce the value of farmland and prevent ordinary agricultural practices, such as fence-building and fertilizer application, in areas that may be regulated wetlands, the groups said.

Zippy Duvall, the American Farm Bureau Federation’s president, praised the Supreme Court’s decision as a victory for property rights and urged the EPA to revise its regulations to align with the ruling.

“Farmers and ranchers share the goal of protecting the resources they’re entrusted with, but they deserve a rule that provides clarity and doesn’t require a team of attorneys to properly care for their land,” he said.