“When the States of Kansas and Colorado were admitted into the Union they were admitted with the full powers of local sovereignty which belonged to other States (Pollard v. Hagan, supra; Shively v. Bowlby, supra; Hardin v. Shedd, 190 U. S., 508, 519); and Colorado by its legislation has recognized the right of appropriating the flowing waters to the purposes of irrigation. Now the question arises between two States, one recognizing generally the common law rule of riparian rights and the other prescribing the doctrine of the public ownership of flowing water. Neither State can legislate for nor impose its own policy upon the other. A stream flows through the two and a controversy is presented as to the flow of that stream. It does not follow, however, that because Congress cannot determine the rule which shall control between the two States, or because neither State can enforce its own policy upon the other, the controversy ceases to be one of a justiciable nature, or that there is no power which can take cognizance of the controversy and determine the relative rights of the two States. Indeed, the disagreement, coupled with its effect upon a stream passing through the two States, makes a matter for investigation and determination by this Court.... “As Congress cannot make compacts between the States as it cannot in respect to certain matters by legislation compel their separate action, disputes between them must be settled either by force or else by appeal to tribunals empowered to determine the right and wrong thereof. Force under our system of government is eliminated. The clear language of the Constitution vests in this Court the power to settle those disputes. We have exercised that power in a variety of instances, determining in the several instances the justice of the dispute. Now, is our jurisdiction ousted, even if, because Kansas and Colorado are States sovereign and independent in local matters, the relations between them depend in any respect upon principles of international law? International law is no alien in this tribunal.... “One cardinal rule, underlying all the relations of the States to each other, is that of equality of right. Each State stands on the same level with all the rest. It can impose its own legislation on no one of the others, and is bound to yield its own views to none. Yet, whenever, as in the case of Missouri v. Illinois, 180 U. S., 208, the action of one State reaches through the agency of natural laws into the territory of another State, the question of the extent and the limitations of the rights of the two States becomes a matter of justiciable dispute between them, and this Court is called upon to settle that dispute in such a way as will recognize the equal rights of both and at the same time establish justice between them. In other words, through these successive disputes and decisions this Court is practically building up what may not improperly be called interstate common law.”