(CN) – The Supreme Court ruled unanimously Monday that any legal challenge of what waters are subject to federal protection must be brought in a trial court, not a federal appeals court.

Adopted in 2015 to replace 1977 standards that had been sowing inconsistent interpretations across the country for decades, the Environmental Protection Agency’s Clean Water Rule expands the definition of “waters of the United States” to include intermittent streams, wetlands and floodplains previously considered to be under the states’ jurisdiction.

As the impetus for its new rule, the EPA cited the need for clean drinking water and clean water as an economic driver and U.S. Supreme Court rulings in 2001 and 2006 in which the justices disagreed about which waters were covered by the law.

“About 117 million Americans – one in three people – get drinking water from streams that lacked clear protection before the Clean Water Rule,” the agency said in a 2015 statement about the new rule. “The health of our rivers, lakes, bays, and coastal waters are impacted by the streams and wetlands where they begin.”

Thirty-one states filed five lawsuits in federal courts throughout the country, claiming the rule trampled state sovereignty.

The Clean Water Rule has never taken effect, as a Sixth Circuit panel granted a stay of the rule in October 2015. It is currently under review by the Trump administration.

The states’ lawsuits were consolidated with cases filed by mining and energy corporations, environmental groups, commercial lobbying organizations, farming groups, and railroads.

The Sixth Circuit panel had been sharply divided on the issue of jurisdiction when it assumed jurisdiction over the case in 2016.

The Supreme Court agreed a year ago to take up the case and clarify the issue of where challenges to the Clean Water Rule must be brought.

On Monday, three months after hearing oral arguments in the case, the nation’s highest court unanimously reversed the Sixth Circuit, ruling that lawsuits against the Obama-era rule must be filed in federal district courts rather than federal appeals courts.

Justice Sonia Sotomayor wrote in a 20-page opinion that the rule defining “waters of the United States” falls outside a federal law that says appeals courts must review EPA actions that enforce certain limitations.

“The WOTUS Rule is not an ‘effluent limitation’—a conclusion the government does not meaningfully dispute. An ‘effluent limitation’ is ‘any restriction . . . on quantities, rates, and concentrations’ of certain pollutants ‘which are discharged from point sources into navigable waters.’ The WOTUS Rule imposes no such restriction,” Sotomayor wrote.

In addition, the rule at issue does not fall under the statutory definition of “other limitation,” the justices found.

“For starters, Congress’ use of the phrase ‘effluent limitation or other limitation’…suggests that an ‘other limitation’ must be similar in kind to an ‘effluent limitation’: that is, a limitation related to the discharge of pollutants. An ‘other limitation,’ for instance, could be a non-numerical operational practice or an equipment specification that, like an ‘effluent limitation,’ restricts the discharge of pollutants, even though such a limitation would not fall within the precise statutory definition of ‘effluent limitation,’” the opinion states.

Sotomayor added, “An ‘other limitation,’ at a minimum, must also be some type of restriction on the discharge of pollutants. Because the WOTUS Rule does no such thing, it does not fit within the ‘other limitation’ language.”

The Supreme Court held that because the relevant federal law doesn’t give appeals courts original or exclusive jurisdiction to review the Clean Water Rule, challenges to the rule must first be filed in federal district courts.