Article I, Section 10, Clause 3:
No State shall, without the Consent of Congress, lay any Duty of Tonnage, keep Troops, or Ships of War in time of Peace, enter into any Agreement or Compact with another State, or with a foreign Power, or engage in War, unless actually invaded, or in such imminent Danger as will not admit of delay.
Once Congress gives its consent to an interstate compact, the compact, "like any other federal statute," becomes the law of the land.  1 Boundaries established by such compacts become binding upon all citizens of the signatory states and are conclusive as to their rights. 2 Private rights may be affected by agreements for the equitable apportionment of the water of an interstate stream, without a judicial determination of existing rights. 3 Valid interstate compacts are within the protection of the Contract Clause, 4 and a
sue and be sued provision therein operates as a waiver of immunity from suit in federal courts otherwise afforded by the Eleventh Amendment. 5 The Supreme Court in the exercise of its original jurisdiction may enforce interstate compacts following principles of general contract law. 6 Congress also has authority to compel compliance with such compacts. 7 Nor may a state read herself out of a compact which she has ratified and to which Congress has consented by pleading that under the state's constitution as interpreted by the highest state court she had lacked power to enter into such an agreement and was without power to meet certain obligations thereunder. The final construction of the state constitution in such a case rests with the Supreme Court. 8