Oklahoma v. New Mexico

Background

Oklahoma and Texas sued New Mexico over how to read the 1951 Canadian River Compact. The main dispute centers on Article IV(b), which limits New Mexico to 200,000 acre-feet of “conservation storage” below Conchas Dam. New Mexico enlarged Ute Reservoir in the 1980s. In 1987 heavy floods spilled about 250,000 acre-feet over Conchas Dam and New Mexico stored a large portion of that water in Ute. Oklahoma and Texas challenged whether the limit applies to reservoir capacity or to water actually stored, and whether spill or return flows must be counted.

Reasoning

The Court agreed with the Special Master that Article IV(b) limits the amount of water actually stored, not the physical capacity of reservoirs. It also held that waters that first enter the river above Conchas but later reach the mainstream below — including spills, releases, seepage, and return flows — count toward the 200,000 acre-foot conservation-storage limit when impounded in New Mexico. The Court overruled Oklahoma’s argument that the limit targets reservoir capacity and rejected New Mexico’s claim that spill waters are exempt. The Court declined to leave the desilting-pool question to the Compact Commission and sent that specific issue back to the Special Master to decide on the merits.

Real world impact

New Mexico may have exceeded its storage rights since 1987 if stored waters exceed 200,000 acre-feet, so it may be required to release or otherwise account for excess water. The ruling protects downstream allocation expectations for Texas and Oklahoma and may affect planning for major projects tied to Canadian River flows. The Court did not enter a final decree and further proceedings will determine remedies and precise effects.

Dissents or concurrances

Chief Justice Rehnquist (joined by three Justices) disagreed with the Court’s reading of Article IV(a), arguing the Compact’s plain text gives New Mexico free use of waters originating above Conchas and that the Court improperly varied the compact’s terms.