The Supreme Court on Thursday dashed the hopes of the Navajo Nation for more running water.

The justices threw out a 9th Circuit Court ruling that held an 1868 treaty confining Navajos to their reservation came with an implied promise that they would have access to water.

The Navajo reservation in Arizona and New Mexico is the nation’s largest, the justices said, and it is desperately short of running water.

But Justice Brett M. Kavanaugh, writing for a 5-4 majority, said the 19th century treaties that established the reservation “did not require the United States to take affirmative steps to secure water for the tribe.”

He said the tribes should look to Congress, not the courts.

“Allocating water in arid regions of the American West is often a zero-sum situation,” he wrote. “And the zero-sum reality of water in the West underscores that courts should stay in their proper constitutional lane… It’s not the judiciary’s role to update the law.”

Justice Amy Coney Barrett cast a key vote for the majority, while Justice Neil M. Gorsuch dissented with the court’s three liberals.

The cases are Arizona vs. Navajo Nation and Dept. of Interior vs. Navajo Nation.

Looming over the cases was the drought-stricken Colorado River and the need to reduce the volume of water taken from the river by California, Arizona and Nevada.

Writing in dissent, Gorsuch said the Navajos were merely seeking to have their water rights seriously considered.

“Today, the Navajo Reservation has become ‘the largest Indian reservation in the United States,’ with over 17 million acres, and over 300,000 members,” he wrote. “Its western boundary runs alongside a vast stretch of the Colorado River. Yet even today, water remains a precious resource. Members of the Navajo Nation use around 7 gallons of water per day for all of their household needs — less than one-tenth the amount the average American household uses. In some parts of the reservation, as much as 91% of Navajo households lack access to water. That deficit owes in part to the fact that no one has ever assessed what water rights the Navajo possess.”

Washington attorney Shay Dvoretsky, representing the Navajo Nation in a losing cause, had argued the court did not need to consider the Colorado River at this stage of the case. “The Nation asks only that the United States, as trustee, assess its people’s needs and develop a plan to meet them,” he argued.

For more than a decade, the Navajo Nation has been fighting its water rights claims in federal court. It won a preliminary victory in the 9th Circuit Court of Appeals in 2021, which said it had a claim for breach of trust, noting that the 1868 treaty referred to agriculture.

“The Nation’s right to farm reservation lands … gives rise to an implied right to the water necessary to do so,” the appeals court said. However, it stopped short of deciding whether this included “rights to the mainstream of the Colorado River or any other specific water sources.”

But last fall, the Supreme Court agreed to hear appeals from both the Interior Department and Arizona that sought to toss out the 9th Circuit’s decision.

U.S. Solicitor Gen. Elizabeth B. Prelogar argued the 1868 treaty said nothing about water and established no specific duties for the government related to water. Moreover, the Navajo Nation has been given water rights from two tributaries of the Colorado River, including San Juan River in Utah, she said.

Lawyers for Arizona, joined by the Metropolitan Water District of Southern California, said the high court’s decrees have allocated the waters from the lower Colorado River, and it is too late for lawsuits that seek new rights to the same water.