Wyoming v. Colorado

Background

Wyoming sued Colorado to enforce a prior Supreme Court decree that divided use of the Laramie River between the two States. Wyoming says Colorado has allowed diversions in Colorado that exceed the amounts set by the earlier decree, has used measuring devices that undercount diversions, and has refused Wyoming access to better measuring equipment. Colorado moved to dismiss, arguing the old decree did not fix all quantities between the States and that the new complaints involve private users, not state action.

Reasoning

The Court reviewed the earlier case and its findings: both States and their users follow the prior-appropriation rule (priority in time governs water rights); the available Laramie supply was found to total 288,000 acre-feet; Wyoming had senior appropriations totaling 272,500 acre-feet; and 15,500 acre-feet remained for Colorado’s Laramie‑Poudre tunnel appropriation. The original decree enjoined Colorado from diverting more than 15,500 acre-feet through the tunnel and recognized Colorado’s Skyline and meadowland appropriations (and later the Wilson Supply ditch). The Court concluded the earlier decree did define the relative rights of the States and their appropriators, and that the present bill sufficiently alleges Colorado’s violations and resulting shortages to Wyoming.

Real world impact

The decision denies Colorado’s motion to dismiss and lets Wyoming press claims to enforce the decree, seek injunctions, and require better measurement or accounting of diversions. The Court allowed Wyoming to amend unclear allegations and ordered Colorado to answer by a set date, so factual proof and possible remedies will now be litigated on the merits.