Water law winds its way slowly through the U.S. legal system, and then often all at once.

On Wednesday, justices will evaluate the arguments from officials in New Mexico, Texas and Colorado on a plan they have put together to resolve a decade-old court case about the Rio Grande, and weigh the federal government’s objections to the states’ agreement.

The original complaint filed by Texas in 2014 alleged that New Mexico groundwater pumping downstream from Elephant Butte was diverting water owed to Texas under the Rio Grande Compact, a decades-old legal agreement.

The states have presented a deal they say resolves the issues. The federal government has asked the court to reject the deal, arguing that it violates the compact and imposes “a host of obligations,” on federally-managed dams, canals and irrigation ditch operations.

Court proceedings start at 8 a.m. MDT and could take several hours. It’s unclear when the justices will issue a response to the oral arguments, but it could be released sometime in June.

The states have responded in previous legal arguments that the remaining issues are “intrastate issues” and can be resolved in lower courts.

Water cases are often adversarial that can take years, often decades to settle, said Reed Benson, a professor on water and environmental issues at the University of New Mexico School of Law.

With the length and complexity of the cases, they often take more than one court opinion, and sometimes more than one special master overseeing the case. But there’s one crucial difference in this case, Benson said: the states are willing to work together.

“If this settlement proves to be able to get it resolved in a decade, it is, I would say, a positive development, as we look at the challenges of interstate water management, as rivers are more and more affected by climate change,” he said. “It’s good to see the states be able to resolve their differences.”

The U.S. Supreme Court allowed the United States to intervene in March 2018, Reed said, which is unusual in river compact disputes.

“Now the United States as intervener, having been let in kind of under special circumstances as the court but now is the one standing in the way of a resolution among the states,” Benson said. “That’s a difficult position for them to be in.”

What could happen?

The special master, the judge overseeing the trial portions of the case, recommended the Supreme Court accept the deal over the federal government’s objections.

Many of the factors allowing the U.S. intervention in the case have been “altered and removed,” wrote Judge Michael Melloy, an 8th Circuit Appeals judge based in Cedar Rapids, Iowa appointed as special master in the Rio Grande case.

“Simply put, the Consent Decree resolves the dispute over the Texas and downstream New Mexico apportionments and protects the Texas apportionment as well as treaty water for Mexico as against New Mexican actions,” he wrote in his report.

But justices are not required to take action based on Melloy’s opinion.

“The Supreme Court justices have gone against the special masters recommendation in many of these cases,” Benson said. “So it carries a little less weight than you might think.”

The justices rejected a previous special master’s 2017 report, when the Court allowed the federal government to intervene.

Regarding the upcoming arguments, 23 states outside of the case wrote to the Court that the federal government was overstepping its limited authority of operating the Rio Grande Project and infringing on state sovereignty to address interstate water compacts.

“The United States asserts an expanded federal role in interstate water compact disputes that, if accepted by the Court, would result in the ability of the United States to insert itself into the equitable apportionment and governance of water among the States,” the filing stated, continuing that the “states have a strong interest in avoiding that result.”

The brief was filed on Dec. 11 by Utah, Alaska, Arizona, Arkansas, Connecticut, Florida, Georgia, Idaho, Indiana, Iowa, Kansas, Louisiana, Michigan, Mississippi, Montana, Nebraska, Oregon, Pennsylvania, South Carolina, South Dakota, Tennessee, Virginia and Wyoming.

It’s unclear what the outcomes of a decision by the Supreme Court would do, whether it requires further settlement talks, or if the settlement fails and returns to a trial.

“It’s very difficult to say what this might mean, either for the future, the litigation, or more broadly. If the United States, you know, should prevail in front of the Supreme Court,” Benson said.