In Colorado River Water Conservation District v. United States, 424 U.S. 800 (1976), the Government proceeded in Federal District Court, bringing suit against some 1,000 nonfederal water users, seeking a declaration of the water rights of certain federal entities and Indian tribes. Shortly thereafter, a defendant in that suit sought to join the United States in a state-court proceeding for the comprehensive adjudication and administration of all water rights within the river system that was the subject of the federal-court suit. The District Court dismissed the federal suit, holding that the abstention doctrine required deference to the state-court proceedings. The Court of Appeals for the Tenth Circuit reversed, holding that the suit of the United States was within the District Court's jurisdiction under 28 U.S. C. 1345 and that abstention was inappropriate. The Court reversed the judgment of the Court of Appeals and affirmed the judgment of the District Court dismissing the complaint. The Court began its analysis by examining the abstention doctrine in its various forms. The Court noted: "Abstention from the exercise of federal jurisdiction is the exception, not the rule. `The doctrine of abstention, under which a District Court may decline to exercise or postpone the exercise of its jurisdiction, is an extraordinary and narrow exception to the duty of a District Court to adjudicate a controversy properly before it. Abdication of the obligation to decide cases can be justified under this doctrine only in the exceptional circumstances where the order to the parties to repair to the State court would clearly serve an important countervailing interest.' " After canvassing the three categories of abstention, we concluded that none of them applied to the case at hand. 424 U.S., at 813-817. Nevertheless, the Court held that the District Court's dismissal was proper on another ground - one resting not on considerations of state-federal comity or on avoidance of constitutional decisions, as does abstention, but on "considerations of `wise judicial administration, giving regard to conservation of judicial resources and comprehensive disposition of litigation.' " The Court noted that " `the pendency of an action in the state court is no bar to proceedings concerning the same matter in the Federal court having jurisdiction,' " and that the federal courts have a "virtually unflagging obligation . . . to exercise the jurisdiction given them." The Court continued: "Given this obligation, and the absence of weightier considerations of constitutional adjudication and state-federal relations, the circumstances permitting the dismissal of a federal suit due to the presence of a concurrent state proceeding for reasons of wise judicial administration are considerably more limited than the circumstances appropriate for abstention. The former circumstances, though exceptional, do nevertheless exist." Id., at 818. The Court declined to prescribe a hard-and-fast rule for dismissals of this type, but instead described some of the factors relevant to the decision. "It has been held, for example, that the court first assuming jurisdiction over property may exercise that jurisdiction to the exclusion of other courts. . . . In assessing the appropriateness of dismissal in the event of an exercise of concurrent jurisdiction, a federal court may also consider such factors as the inconvenience of the federal forum; the desirability of avoiding piecemeal litigation; and the order in which jurisdiction was obtained by the concurrent forums. No one factor is necessarily determinative; a carefully considered judgment taking into account both the obligation to exercise jurisdiction and the combination of factors counselling against that exercise is required. Only the clearest of justifications will warrant dismissal." Id., at 818-819. In Colorado River Water Conserv. Dist. v. United States, 424 U.S. 800, 96 S.Ct. 1236, 47 L.Ed.2d 483 (1976), the Supreme Court announced that a federal court may dismiss an action because of parallel state court litigation only under "exceptional" circumstances. 424 U.S. at 818, 96 S.Ct. at 1246. Indeed, "only the clearest of justifications will warrant dismissal." Id. at 819, 96 S.Ct. at 1247. The Court set out four factors to be considered in determining whether dismissal on the grounds of exceptional circumstances is appropriate: (1) whether one of the courts has assumed jurisdiction over property; (2) the inconvenience of the federal forum; (3) the potential for piecemeal litigation; (4) the order in which the forums obtained jurisdiction. Id. at 818, 96 S.Ct. at 1246-1247. In Colorado River Water Conservation Dist. v. United States, 424 U.S. 800 (1976), the Court noted that there were principles unrelated to considerations of proper constitutional adjudication and regard for federal-state relations which govern in situations involving the contemporaneous exercise of concurrent jurisdictions, either by federal courts or by state and federal courts. 424 U.S. at 817. According to the Court, these principles rest on considerations of wise judicial administration, giving regard to conservation of judicial resources and comprehensive disposition of litigation. Id. In general, the pendency of an action in state court is no bar to proceedings in federal court concerning the same matter. Id. As between two federal district courts, the general rule is that duplicative litigation should be avoided. Id. The Court explained that the difference in approach between federal-state concurrent jurisdiction and wholly federal concurrent jurisdiction stemmed from the virtually unflagging obligation of the federal courts to exercise the jurisdiction given them. Id. In Colorado River, the Supreme Court identified the inconvenience of the federal forum as a factor for the federal court to consider in deciding whether to dismiss a federal court action because of a concurrent state proceeding. 424 U.S. at 818. In Colorado River, the Court referred to the inconvenience of trying the case in the federal district court in Denver, 300 miles from the disputed area and from the Colorado state court with jurisdiction over that area. 424 U.S. at 820. In Colorado River Water Conservation District v. United States, 424 U.S. 800 (1976), the Court recognized a narrow rule of abstention governing controversies involving federal water rights. The Court stated that in light of "the virtually unflagging obligation of the federal courts to exercise the jurisdiction given them," id., at 817, "only the clearest of justifications," id., at 819, will warrant abstention in favor of a concurrent state proceeding.