In a 5-4 decision in a case that impacts Rio Grande River water distribution, the Supreme Court nullified a water-sharing agreement between Texas and New Mexico because the deal would have denied U.S. interests in how the Rio Grande Project is operated.

In the case Texas v. New Mexico and Colorado, Texas sued New Mexico on the claim that excessive groundwater pumping in New Mexico was depleting supplies of Rio Grande River water that would otherwise be allocated to Texas, so New Mexico breached the Rio Grande Compact.

The federal government agreed that New Mexico breached the Rio Grande Compact and that New Mexico’s breach of the compact harmed U.S. interests on the Rio Grande River. 

The case was argued before the Supreme Court on March 20, 2024, at which time New Mexico argued the U.S. was not a party to the interstate agreement between Colorado, New Mexico, and Texas—known as the Rio Grande Compact—and that the “special master” appointed by the Supreme Court in 2013 agreed.

However, Texas and New Mexico agreed to a proposed consent decree that would resolve the dispute and codify a methodology for determining each state’s allocation of water from the Rio Grande River. 

Nonetheless, Chief Justice John Roberts, along with Associate Justices Ketanji Brown Jackson, Sonia Sotomayor, Elena Kagan, and Brett Kavanaugh, rejected New Mexico’s argument that the U.S. was not a party to the Rio Grande Compact, with the majority opinion saying: “Parties who chose to resolve litigation through settlement may not dispose of the claims of a third party.”

Furthermore, the majority opinion cites a lawsuit in 2013 that mirrors the recent case in that in 2013, Texas filed suit against Colorado and New Mexico, alleging excessive groundwater pumping in New Mexico was a violation of the compact. The U.S. “sought to intervene” in the 2013 case, and the Supreme Court allowed it to do so.

In addition, the majority opinion in the latest case—issued June 21, 2024—quotes the decision in the 2013 lawsuit, saying, “The federal government has its own distinct interests in holding New Mexico to its obligations under the compact, as the compact is ‘inextricably intertwined’ with the United States’ operation of the Rio Grande Project.”

However, the dissenting opinion, written by Associate Justice Neil M. Gorsuch, says previous Supreme Court decisions in matters related to the Rio Grande Compact approved permitting the U.S. to intervene in disputes between state signatories of the compact because such intervention “would allow it (the U.S.) to ensure its treaty obligations with Mexico were honored.” But, those previous decisions also “warned that permission to intervene should not be confused for the license” to do so, the dissenting opinion says.

Furthermore, “the court’s (current) decision defies 100 years of this court’s water law jurisprudence. And it represents a serious assault on states' power to govern users' water rights in their jurisdictions,” the dissenting opinion says. 

Joining Gorsuch in the dissent were Associate Justices Clarence Thomas, Samuel Alito, and Amy Coney Barrett.

Read both opinions in Texas v. New Mexico and Colorado.