Mississippi v. Tennessee

Mississippi is entitled only to the remedy of equitable apportionment, and since its complaint expressly disclaimed equitable apportionment, its complaint is dismissed without leave to amend. Chief Justice John Roberts authored the unanimous opinion of the Court. Equitable apportionment is a judicial remedy that seeks to fairly allocate a shared water resource between two or more states. Although the Court has not previously considered whether the doctrine of equitable apportionment applies to interstate aquifers, it has applied the remedy when transboundary water resources were at issue, and the same reasoning applies. First, like other transboundary water resources, the Middle Claiborne Aquifer has a “multistate character.” Second, it contains water that naturally flows between the states. And third, actions taken in Tennessee affect the portion of the aquifer that underlies Mississippi. For these reasons, equitable apportionment applies to the waters of the Middle Claiborne Aquifer.