The U.S. Supreme Court case Colorado River Water Conservation District et al. v. United States in 1975 revolved around the issue of whether federal or state courts should have jurisdiction over a water rights dispute in Colorado. The United States, on behalf of two Indian tribes, filed suit against various entities including the State of Colorado and several water conservation districts to establish its reserved water rights for tribal lands under federal law. The defendants argued that this was an issue for state court as it involved complex issues related to local water laws and policies which were better understood by a state court rather than a federal one. In its decision, the Supreme Court held that while there is generally a "virtually unflagging obligation" for federal courts to exercise their jurisdiction, there are certain exceptional circumstances where it may be appropriate for them to defer to ongoing parallel proceedings in state courts based on considerations such as avoiding piecemeal litigation and respecting principles of comity among different judicial systems. However, upon reviewing these factors in light of this particular case's facts and context, the Court concluded that they did not justify abstention here because no similar comprehensive adjudication was pending at the time when this lawsuit was initiated.

In the dissenting opinion for Colorado River Water Conservation District v. United States, Justice Brennan disagreed with the majority's decision to abstain from exercising jurisdiction in a case involving water rights in Colorado. He argued that federal courts have an obligation to hear cases within their jurisdiction and should not defer to state courts unless there are exceptional circumstances. In this case, he did not believe such circumstances existed because both federal and state law were relevant to resolving the dispute. Furthermore, he expressed concern that deferring too often could undermine public confidence in federal courts and create confusion about when they will exercise their authority. Finally, he noted that while managing water resources is indeed complex and important work typically left up to states, it does not justify abdicating responsibility when those issues come before a federal court.