alent to one-half of the mean flow at the Hesperus station for the preceding day, but not to exceed one hundred cubic feet per second. "3. Whenever the flow of the river is so low that in the judgment of the State engineers of the States the greatest beneficial use of its waters may be secured by distributing all of its water successively to the lands in each State in alternating periods, in lieu of delivery of water as provided in the second paragraph of this article, the use of the waters may be so rotated between the two States in such manner, for such periods, and to continue for such time as the State Engineers may jointly determine." For the administration of water rights, Colorado and New Mexico each set up an administrative system with the State Engineers at its head. The State Engineers agreed that, in order to put the water to its most efficient use in the hot summer months of 1928, when the river was very low, the whole of the available supply should be rotated between the two States. In other words, that each State should be permitted to enjoy the entire flow of the river during alternating ten-day periods. During the ten days commencing June 24, 1928, all the water of the river (except small amounts diverted in Colorado for domestic and stock requirements) was thus allowed to pass to New Mexico; and during the succeeding ten-day period all the water in the stream was similarly allowed to be diverted in Colorado. The defendant water officials contend that in so rotating the water of the stream they administered it as required by the Compact and wisely. The La Plata River rises in the mountains of Colorado, flows in a southerly direction until it reaches the boundary of New Mexico and in the latter State until it empties into the San Juan River. The stream is non-navigable; has a narrow watershed; and a large run-off in the early spring. Then the quantity flowing begins to fall rapidly; 81638-38-7 Opinion of the Court 304 U.S. and during the summer months little water is available for irrigation. In each State the water of the stream has long been used for irrigation; and each adopted the socalled appropriation doctrine of water use. Under that doctrine the first person who acts toward the diversion of water from a natural stream and the application of such water to a beneficial use has the first right, provided he diligently continues his enterprise to completion and beneficially applies the water. The rights of subsequent appropriations are subject to rights already held in the stream. The relative rights of all claimants to divert in Colorado water from the La Plata River were adjudicated in a proceeding under the Colorado statutes. By decree therein of January 12, 1898 (and later amended) the Ditch Company was declared entitled to divert 391⁄4 cubic feet of water per second, subject to five senior priorities aggregating 19 second feet. On June 24, 1928, there was in the stream, at the recognized Colorado gauging station, 57 second feet of water. The Ditch Company claimed that by reason of the 1898 decree it was entitled to all the water in the stream except that required to satisfy the Colorado priorities. If it had been permitted to draw all that water, none would have been available to the New Mexico water claimants, who, under similar laws, had made appropriations. Some of them were earlier in date than the Ditch Company's. 'Colorado Constitution, Art. XVI, § 5, provides: "The water of every natural stream, not heretofore appropriated, within the state of Colorado, is hereby declared to be the property of the public, and the same is dedicated to the use of the people of the state, subject to appropriation as hereinafter provided." Article XVI, § 6, provides in part: "The right to divert unappropriated waters of any natural stream to beneficial uses shall never be denied. Priority of appropriation shall give the better right as between those using the water for the same purpose." For the law of New Mexico, see its Constitution, Art. XVI, §§ 2 and 3. 92 Opinion of the Court. The case was first heard in the District Court on evidence in 1930. The Ditch Company objected at the trial to the admission or consideration of the Compact. It insisted that the Compact attempted to surrender to New Mexico, and thus destroy, vested property rights of Colorado citizens; that this is a violation of the obligations of its contract; and that the Compact in so far as it "applies or is intended to apply to private rights of the individuals or citizens of Colorado, or to be used as a defense of or justification for the acts of the State Engineer or his subordinates in interfering with or violating the private rights of citizens of Colorado, or in attempting to disregard, ignore or set aside the decrees of this [District] Court for the distribution of water in accordance with the decrees, is unconstitutional and void" in violation of the due process clauses of the Fifth and Fourteenth Amendments of the Federal Constitution and of § 25 of the Constitution of Colorado. The District Court overruled the objection; found in substance the facts stated above; held that the Compact justified the action of defendants; and entered a decree that the bill be dismissed, each party to bear its own costs. That judgment was reversed by the Supreme Court of the State (one judge dissenting), La Plata River & Cherry Creek Ditch Co. v. Hinderlider, 93 Colo. 128; 25 P. 2d 187. The opinion declared: "There is not the slightest pretense, either in this compact itself or in the proceedings leading up to it, to a decision of the question of what water Colorado owns, or what water New Mexico owns, or what their respective citizens own. It is a mere compromise of presumably conflicting claims, a trading therein, in which the property of citizens is bartered, without notice or hearing and with no regard to vested rights." An appeal to this Court was dismissed for want of final judgment below. Hinderlider v. La Plata River & Cherry Opinion of the Court. 304 U.S. Creek Ditch Co., 291 U. S. 650. The case was then retried by the District Court on the same pleadings and evidence; and, pursuant to the opinion of the Supreme Court of Colorado, a decree was entered which, after reciting in substance the facts above stated, declared: "6. That the said La Plata River Compact, entered into between the States of Colorado and New Mexico with the consent of the Congress of the United States of America, does not constitute a defense to the actions of said defendant water officials complained of by plaintiff, and is not available to said defendant water officials, as a legal defense or justification, for their acts in closing and shutting down the headgate of plaintiff and in depriving the said plaintiff, thereby, of its right to the use of the waters from said La Plata River for irrigation purposes, as provided by the terms and provisions of said decree of adjudication of January 12, 1898." The decree specifically: "(3) Enjoined and commanded [the defendants] to permit the diversion through the plaintiff's headgate [of] water for plaintiff's ditch in accordance with the terms of said decree at any and all times when there is water in said stream to which said decree, under its terms and conditions would apply; . . ." This second judgment of the trial court was affirmed by the Supreme Court of the State; an additional opinion being delivered by the court, and a dissent by a different justice. 101 Colo. 73; 70 P. 2d 849. An appeal to this Court was allowed by the Acting Chief Justice of the State. Pursuant to the Act of Congress, August 24, 1937, c. 754, 50 Stat. 751, the attention of the Attorney Gen * The first judgment in the trial court was entered June 16, 1930; the first judgment of the Supreme Court of Colorado on July 3, 1933; the dismissal by this Court of the first appeal on March 12. 1934; the second judgment in the trial court on May 12, 1936; the second judgment of the Supreme Court of Colorado on July 6, 1937. 1 26 92 Opinion of the Court. eral of the United States was directed to the contention that the validity of a federal statute is involved, 302 U. S. 646. He filed memoranda in which he contended that: "(1) this Court is included in the courts to which Section 1 of the Act of August 24, 1937, is applicable; (2) the constitutionality of the compact is drawn in question whether or not a decision on this point is necessary; (3) a compact is an Act of Congress; and (4) it is an Act 'affecting the public interest.'" Opposing some of the views expressed by the Attorney General, a brief was filed on behalf of Delaware, Maryland, New Jersey, New York, Virginia, the Port of New York Authority and the Delaware River Joint Commission. The Ditch Company moved to dismiss the appeal, contending, among other things, that the mere fact that the Compact was approved by Congress does not make it a federal statute within the meaning of the jurisdictional act authorizing appeals. Decision on the motion to dismiss was postponed to the hearing on the merits. For reasons to be stated, we are of opinion that the case is not reviewable on appeal; that it presents a federal question reviewable on certiorari; that because of its importance certiorari should be granted; and that the judgment must be reversed. First. As the La Plata River flows from Colorado into New Mexico and in each State the water is used beneficially, it must be equitably apportioned between the two. The decision below in effect ignores that rule. It holds immaterial the fact that the acts complained of were being done in compliance with the Compact, and does so on the ground that the Compact in authorizing diversion and rotation violated rights awarded by the January 12, 1898 decree in the Colorado water proceeding; holds that the decree awarded to the Ditch Company the right to divert from the river 394 cubic feet per second (subject |