Texas v. New Mexico

Docket Number: 141, Orig.
Citation: 608 U.S. 346
Term: October Term 2025
Decided: May 26, 2026
Author: D

AI-Generated Summary

Case Information:

Case Name: Texas v. New Mexico, et al.
Docket Number: No. 141, Orig.
Dates: Final Decree Entered May 26, 2026 (no argument date specified)
Lower Court: Original jurisdiction; entered on receipt of the Fourth Interim Report of the Special Master (Hon. D. Brooks Smith)

Facts of the Case: The case concerns the equitable apportionment of Rio Grande waters under the Rio Grande Compact (approved by Congress in 1939) among Colorado, New Mexico, and Texas. The dispute centers on New Mexico’s delivery obligations to Texas below Elephant Butte Reservoir, measured at the El Paso Gage, including the effects of groundwater pumping, surface-water use, and Project operations. The Special Master’s Fourth Interim Report proposed a consent decree resolving the apportionment issues. The decree incorporates detailed technical appendices defining the Effective El Paso Index (EEPI) methodology, including Index Obligation, Index Delivery, Annual and Accrued Index Departures, caps, triggers, and accounting procedures. The Court entered the proposed decree as Appendix A to the report and discharged the Special Master.

Legal Issues Presented: The primary issue is the proper division of Rio Grande water between New Mexico and Texas below Elephant Butte Reservoir consistent with the Compact’s equitable apportionment (approximately 57% New Mexico / 43% Texas based on authorized Project acreage). The decree clarifies Compact compliance through an index-based methodology without modifying the Compact itself. It addresses calculation of annual obligations and deliveries, handling of departures (positive/negative), limits on accrued negative departures, water-management triggers, aridity adjustments, spill extinguishments, and data-reporting protocols. No adversarial arguments are presented; the decree reflects unanimous agreement of the Compacting States.

The Court’s Decision (Main Opinion):

Author & Type: Per Curiam decree (unanimous consent decree of the Court).
Holding: The proposed consent decree is entered as the final resolution of the Compact apportionment dispute. New Mexico must manage water to satisfy the Effective El Paso Index (EEPI) requirements; compliance with the decree constitutes compliance with the Compact regarding division below Elephant Butte Reservoir.
Legal Reasoning: The decree establishes precise definitions and formulas (detailed in Appendix 1) for Index Obligation (regression-based on D2 Period Caballo Releases plus Texas Mesilla depletions, adjusted for aridity), Index Delivery (streamflow at El Paso Gage plus Texas Mesilla depletions minus Mexico deliveries and Excess Flow), Annual/Accrued Index Departures, caps (e.g., 67,500 af positive; 112,500/90,000 af negative), limits (150,000/120,000 af accrued negative), triggers for management actions, extinguishment on spills or high Texas carryover, and accounting procedures. It preserves Compact rights, U.S. treaty obligations to Mexico, and tribal rights while creating no third-party beneficiaries. Appendices control technical methodology; the decree language controls in case of conflict.
Disposition: Consent decree entered; Special Master discharged.

Concurring Opinion(s) (if any): None.

Dissenting Opinion(s) (if any): None.

Potential Significance: The decree provides a binding, enforceable index-based framework for ongoing Compact compliance, including specific numerical caps, triggers, adjustments, and data protocols that will govern future water accounting and potential enforcement motions. It retains the Court’s jurisdiction for future modifications or relief.

This summary was generated by AI and may contain inaccuracies. Refer to the official source document for the authoritative text.

Key terms: Rio Grande Compact, Water Apportionment, Interstate Water Dispute