This October Term, the U.S. Supreme Court will be asked to weigh in on three and possibly all four of its pending original jurisdiction controversies over interstate waters. The Court’s past judgments and opinions have established little in the way of “federal common law” governing the states’ interests in shared waters. But they have established this much: these interests vest in states-as-states directly under the U.S. Constitution, even if the Court itself is reluctant to specify the interests with much precision or to enjoin violations thereof.