Texas v. New Mexico
Wikipedia · Justia (with opinion) · Docket · oyez.org
Argued on Oct 5, 2020.Decided on Dec 14, 2020.
Petitioner: Texas.Respondent: New Mexico.
Advocates: Kyle D. Hawkins (for the State of Texas)
Jeffrey J. Wechsler (for the State of New Mexico)
Masha G. Hansford (for the United States, as amicus curiae, supporting New Mexico)
Facts of the case (from oyez.org)
Texas and New Mexico entered into the Pecos River Compact to resolve disputes about the Pecos River, which traverses both states. A River Master performs annual calculations of New Mexico's water delivery to ensure it complies with its Compact obligations. A party may seek the Supreme Court's review of the River Master's calculations within 30 days of its final determination.
In 2014 and 2015, after heavy rainfall, a federally owned reservoir in New Mexico retained large amounts of flood waters in the Pecos Basin. When the reservoir's authority to hold the water expired, it began to release the water. Texas could not use the released water, so it also released the water to make room for water flowing from New Mexico.
When the River Master calculated and reported New Mexico's obligations for 2014 and 2015, it did not reduce Texas's rights to delivery based on the evaporation of water stored in the federal reservoir in New Mexico that Texas could not use. The 30-day review period lapsed, and New Mexico filed no objection. However, in 2018, New Mexico filed a motion challenging the River Master's calculations. Rather than dismiss the untimely objection, the River Master modified the governing manual to allow retroactive changes to final reports, gave that modification retroactive effect, and amended the 2015 report to credit New Mexico for the evaporative loss.

Question
1. Did the River Master err in retroactively amending the River Master Manual?
2. Did the River Master err in charging Texas for evaporative losses?

Conclusion
Texas’s motion to review the Pecos River Master’s determination is denied. Justice Brett Kavanaugh authored the majority opinion of the Court.
New Mexico’s motion for credit for the evaporated water was not untimely. As Texas and New Mexico agreed to postpone the River Master’s resolution of the evaporated water issue, neither party may now object to the negotiation procedure the River Master outlined for resolving the dispute. Additionally, Texas’s request that Net Mexico store water at a facility in New Mexico was based on Texas’s understanding that the water belonged to Texas.
Justice Samuel Alito filed an opinion concurring in the judgment in part and dissenting in part. He agreed with the Court’s rejection of Texas’s argument that New Mexico forfeited any objection to the River Master’s 2014 report because it did not file an objection by the deadline imposed by the amended decree. However, he would vacate and remand the case for the River Master to redo his analysis in accordance with the relevant terms of the amended decree and the manual.
Justice Amy Coney Barrett took no part in the consideration or decision of this case.