US SUPREME COURT DECISIONS

The Vermejo River -- which originates in southern Colorado but is located primarily in New Mexico -- is at present fully appropriated by users in New Mexico. Colorado seeks an equitable apportionment of the river's water in order to divert water for proposed uses. The Special Master, after a trial, recommended in his report that Colorado be permitted a diversion of 4,000 acre-feet per year. The Special Master recognized that strict application of the rule of prior appropriation would not permit any diversion. In applying the principle of equitable apportionment, however, he did not focus exclusively on the rule of priority, but apparently rested his recommendation on the alternative grounds that New Mexico could compensate for some or all of the Colorado diversion through reasonable water conservation measures, and that the injury, if any, to New Mexico would be outweighed by the benefit to Colorado from the diversion. New Mexico filed exceptions to the Special Master's report.

Held:

1. The flexible principle of equitable apportionment applies to a State's claim to divert water for future uses, and the criteria relied upon by the Special Master comport with this Court's prior cases. Pp. 183188.

(a) When, as in this case, both States recognize the doctrine of prior appropriation, priority becomes the guiding principle, but not the sole criterion, in determining an equitable apportionment. Pp. 459 U. S. 183-184.

(b) While the equities supporting the protection of established, senior uses are substantial, it is also appropriate to consider additional factors relevant to a just apportionment, such as the conservation measures available to both States here and the balance of harms and benefits to the States that might result from the diversion sought by Colorado. Pp. 459 U. S. 184-187.

(c) A State seeking a diversion for future uses must demonstrate by clear and convincing evidence that the benefits of the diversion substantially outweigh the harm that might result. Pp. 459 U. S. 187-188.

2. However, the Special Master's report does not contain sufficient factual findings to enable this Court to assess the correctness of his application of the principle of equitable apportionment to the facts of this chanrobles.com-red

Page 459 U. S. 177

case. Accordingly, this Court remands for additional findings, including specific findings relating to the Special Master's reliance on the factors of the availability of conservation measures and the weighing of the harms and benefits that would result from the diversion. Pp. 459 U. S. 189-190.

Remanded for further findings.

MARSHALL, J., delivered the opinion of the Court, in which BURGER, C.J.,and BRENNAN, WHITE, BLACKMUN, REHNQUIST, and STEVENS, JJ., joined. BURGER, C.J.,filed a concurring opinion, in which STEVENS, J., joined, post, 459 U. S. 190. O'CONNOR, J., filed an opinion concurring in the judgment, in which POWELL, J., joined, post, 459 U. S. 191.