The Supreme Court ruled against the Navajo Nation on Thursday in a dispute involving water from the drought-stricken Colorado River.

States that draw water from the river — Arizona, Nevada and Colorado — and water districts in California that are also involved in the case had urged the court to decide for them, which the justices did in a 5-4 ruling. Colorado had argued that siding with the Navajo Nation would undermine existing agreements and disrupt the management of the river.

The Biden administration had said that if the court were to come down in favor of the Navajo Nation, the federal government could face lawsuits from many other tribes.

Lawyers for the Navajo Nation had characterized the tribe’s request as modest, saying they simply were seeking an assessment of the tribe’s water needs and a plan to meet them.

The facts of the case go back to treaties that the tribe and the federal government signed in 1849 and 1868. The second treaty established the reservation as the tribe’s “permanent home” — a promise the Navajo Nation says includes a sufficient supply of water. In 2003 the tribe sued the federal government, arguing it had failed to consider or protect the Navajo Nation’s water rights to the lower portion of the Colorado River.

Writing for a majority made up of conservative justices, Justice Brett Kavanaugh explained that “the Navajos contend that the treaty requires the United States to take affirmative steps to secure water for the Navajos — for example, by assessing the Tribe’s water needs, developing a plan to secure the needed water, and potentially building pipelines, pumps, wells, or other water infrastructure.”

But, Kavanaugh said, “In light of the treaty’s text and history, we conclude that the treaty does not require the United States to take those affirmative steps.”

Kavanaugh acknowledged that water issues are difficult ones.